Document:

<PAGE>   1
                                                                Exhibit 10(o)(5)

                             FOURTH AMENDMENT TO THE
                     PEOPLES HERITAGE FINANCIAL GROUP, INC.
                              THRIFT INCENTIVE PLAN

         The Peoples Heritage Financial Group, Inc. Thrift Incentive Plan (the
"Plan") was last amended and restated effective generally January 1, 1996, and
subsequently amended by a First Amendment, a Second Amendment, and a Third
Amendment effective as of the dates set forth in the respective amendments, and
shall be further amended as set forth herein.

         1. The terms used in this Fourth Amendment shall have the meanings set
forth in the Plan unless the context indicates otherwise.

         2. Section 8.5(c)(i) shall be amended to read in its entirety as
follows:

                           "(i) A Participant's benefits shall be distributed
         commencing not later than the required beginning date or shall be
         distributed, beginning not later than the required beginning date, over
         a period not extending beyond the life expectancy of such Participant
         or the life expectancy of the Participant and the joint annuitant of
         the Participant. For purposes of this Paragraph (c), the "required
         beginning date" means the following, effective January 1, 1998:

                                            "(A) For a Participant who attains
                           age seventy and one half (70 1/2) before January 1,
                           1999, April 1 of the calendar year following the
                           calendar year in which the Participant attains age
                           seventy and one half (70 1/2).

                                            "(B) For a Participant who attains
                           age seventy and one half (70 1/2) after December 31,
                           1998, April 1 of the calendar year following the
                           later of (1) the calendar year in which the
                           Participant attains age seventy and one half
                           (70 1/2), or (2) the calendar year in which the
                           Participant retires; provided that this clause
                           (2) shall not apply in the case of a Participant who
                           is a five percent (5%) owner (within the meaning of
                           Section 416(i) of the Code) with respect to the Plan
                           Year ending in the calendar year in which the
                           Participant attains age seventy and one half
                           (70 1/2); and provided further that in the case of a
                           Participant to whom this clause (2) applies and who
                           retires in a calendar year after the calendar year in
                           which he or she attains age seventy and one half
                           (70 1/2), the Participant's Accrued Benefit shall be
                           actuarially increased, in the manner prescribed by
                           the Secretary of the Treasury, to take into account
                           the period after age seventy and one half (70 1/2) in
                           which the Participant was not receiving any benefits
                           under the Plan."

         3. Section 14.5 shall be amended by adding the following sentence at
the end thereof:

         "Effective January 1, 1998, the "required beginning date" for any
         distribution under this Section shall be determined under Section
         8.5(c)(i)."

         4. Appendix A shall be amended to read in its entirety as follows:

<PAGE>   2

                     "PEOPLES HERITAGE FINANCIAL GROUP, INC.
                              THRIFT INCENTIVE PLAN
                                   APPENDIX A

                  "Each of the following Schedules sets forth certain benefits,
         rights, and features under Predecessor Plans that remain in effect
         solely with respect to a Participant's Predecessor Plan Account in
         accordance with Article XIV of the Plan, and, to the extent applicable
         with respect to any Predecessor Plan Participant, for purposes of
         Section 14.6 of the Plan.

<TABLE>
<CAPTION>
         SCHEDULE                               PREDECESSOR PLAN                      PLAN AFFILIATION DATE
         --------                               ----------------                      ---------------------
<S>                          <C>                                                      <C>
         1                   Mid Maine Savings Bank, FSB 401(k) Savings Plan          January 1, 1996
         2                   Bank of New Hampshire Corporation Tax Deferred Savings   July 1, 1996
                             & Investment Plan
         3                   SBERA 401(k) Plan As Adopted By Family  Mutual  Savings  April 1, 1997
                             Bank
         4                   Atlantic Bank 401(k) Profit Sharing Plan                 December 1, 1997
         5                   Concord Savings Bank 401(k) Plan                         November 1, 1998
         6                   CFX Corporation 401(k) Plan                              December 15, 1998
</TABLE>

                                 "SCHEDULE NO. 1
                                 RELATING TO THE
                 MID MAINE SAVINGS BANK, FSB 401(K) SAVINGS PLAN

                  "The Mid Maine Savings Bank, FSB 401(k) Savings Plan (the "Mid
         Maine Plan") was merged into the Plan effective January 1, 1996. The
         provisions of the Mid Maine Plan remaining in effect under Article XIV
         of this Plan with respect to the Predecessor Plan Account of a
         participant in the Mid Maine Plan on December 31, 1995, shall be as set
         forth in the Mid Maine Plan as in effect on such date, which is
         incorporated by reference herein; except that Section 8.5(c) of this
         Plan shall apply to the determination of the required beginning date
         for distribution of the Predecessor Plan Account for any Participant
         who attains age seventy and one half (70 1/2) after December 31, 1998.

                                 "SCHEDULE NO. 2
                RELATING TO THE BANK OF NEW HAMPSHIRE CORPORATION
                     TAX DEFERRED SAVINGS & INVESTMENT PLAN

                  "The Bank of New Hampshire Corporation Tax Deferred Savings &
         Investment Plan (the "Bank of New Hampshire Plan") was merged into the
         Plan effective July 1, 1996. The provisions of the Bank of New
         Hampshire Plan remaining in effect under Article XIV of this Plan with
         respect to the Predecessor Plan Account of a participant in the Bank of
         New Hampshire Plan on June 30, 1996, shall be as set forth in the Bank
         of New Hampshire Plan as in effect on such date, which is incorporated
         by reference herein; except that Section 8.5(c) of this Plan shall
         apply to the determination of the required beginning date for
         distribution of the Predecessor Plan Account for any Participant who
         attains age seventy and one half (70 1/2) after December 31, 1998.

                                       2

<PAGE>   3

                                 "SCHEDULE NO. 3
                        RELATING TO THE SBERA 401(K) PLAN
                    AS ADOPTED BY FAMILY MUTUAL SAVINGS BANK

                  "The SBERA 401(k) Plan as Adopted By Family Mutual Savings
         Bank (the "Family Bank Plan") was merged into the Plan effective April
         1, 1997. The provisions of the Family Bank Plan remaining in effect
         under Article XIV of this Plan with respect to the Predecessor Plan
         Account of a participant in the Family Bank Plan on March 31, 1997,
         shall be as set forth in the Family Bank Plan as in effect on such
         date, which is incorporated by reference herein; except that Section
         8.5(c) of this Plan shall apply to the determination of the required
         beginning date for distribution of the Predecessor Plan Account for any
         Participant who attains age seventy and one half (70 1/2) after
         December 31, 1998.

                                 "SCHEDULE NO. 4
            RELATING TO THE ATLANTIC BANK 401(K) PROFIT SHARING PLAN

                  "The Atlantic Bank 401(k) Profit Sharing Plan (the "Atlantic
         Bank Plan") shall be merged into the Plan effective December 1, 1997.
         The provisions of the Atlantic Bank Plan remaining in effect under this
         Plan with respect to the Predecessor Plan Account of a participant in
         the Atlantic Bank Plan on November 30, 1997, shall be as set forth in
         the Atlantic Bank Plan as in effect on such date, which is incorporated
         by reference herein; except that Section 8.5(c) of this Plan shall
         apply to the determination of the required beginning date for
         distribution of the Predecessor Plan Account for any Participant who
         attains age seventy and one half (70 1/2) after December 31, 1998.

                                 "SCHEDULE NO. 5
                RELATING TO THE CONCORD SAVINGS BANK 401(K) PLAN

                  "The Concord Savings Bank 401(k) Plan (the "Concord Plan")
         shall be merged into the Plan effective November 1, 1998. The
         provisions of the Concord Plan remaining in effect under this Plan with
         respect to the Predecessor Plan Account of a participant in the Concord
         Plan on October 31, 1998, shall be as set forth in the Concord Plan as
         in effect on such date, which is incorporated by reference herein;
         except that Section 8.5(c) of this Plan shall apply to the
         determination of the required beginning date for distribution of the
         Predecessor Plan Account for any Participant who attains age seventy
         and one half (70 1/2) after December 31, 1998.

                                 "SCHEDULE NO. 6
                   RELATING TO THE CFX CORPORATION 401(K) PLAN

                  "The CFX Corporation 401(k) Plan (the "CFX Plan") shall be
         merged into the Plan effective December 15, 1998. The provisions of the
         CFX Plan remaining in effect under this Plan with respect to the
         Predecessor Plan Account of a participant in the CFX Plan on December
         14, 1998, shall be as set forth in the CFX Plan as in effect on such
         date, which is incorporated by reference herein; except that Section
         8.5(c) of this Plan shall apply to the determination of the required
         beginning date for distribution of the Predecessor Plan Account for any
         Participant who attains age seventy and one half (70 1/2) after
         December 31, 1998."

                                       3

<PAGE>   4

         5. This Fourth Amendment shall be generally effective January 1, 1998,
except that provisions relating to the merger of the Concord Plan into the Plan
shall be effective November 1, 1998, and provisions relating to the merger of
the CFX Plan into the Plan shall be effective December 15, 1998.

         IN WITNESS WHEREOF, to record the adoption of this Fourth Amendment as
of the effective dates stated herein, Peoples Heritage Financial Group, Inc. has
caused this instrument to be executed by its duly authorized officer this 7th
day of December, 1998.

                                          PEOPLES HERITAGE FINANCIAL GROUP, INC.

                                          By /s/ Susan G. Shorey
                                          --------------------------------------
                                          Its Vice President

                                       4<PAGE>   1

                                                                Exhibit 10(o)(6)

                             FIFTH AMENDMENT TO THE
                     PEOPLES HERITAGE FINANCIAL GROUP, INC.
                              THRIFT INCENTIVE PLAN

         The Peoples Heritage Financial Group, Inc. Thrift Incentive Plan (the
"Plan") was last amended and restated effective generally January 1, 1996, and
subsequently amended by First, Second, Third, and Fourth Amendments effective as
of the dates set forth in the respective amendments, and shall be further
amended as set forth herein.

         1. The terms used in this Fifth Amendment shall have the meanings set
forth in the Plan unless the context indicates otherwise.

         2. Section 6.3(c) shall be amended to read in its entirety as follows:

                           "(c) Effective January 1, 1998, no loan shall be made
         in an amount less than One Thousand Dollars ($1,000), nor shall a loan
         be made if a Participant has any other loan outstanding with respect to
         his or her Aggregate Account under the Plan. Notwithstanding the
         preceding sentence to the contrary, a loan may be made in an amount
         less than One Thousand Dollars ($1,000) if the Participant is also a
         participant or beneficiary who is a "party in interest" as defined in
         Section 3(14) of ERISA with respect to the SIS Bank Employees' Savings
         Incentive Plan ("SIS Plan"); his or her Aggregate Account balance under
         this Plan is not sufficient to permit a loan to be made in the amount
         of at least One Thousand Dollars ($1,000); and each of the following
         requirements is satisfied:

                                    (i) the sum of the Participant's account
                  balance under the SIS Plan plus the Participant's Aggregate
                  Account balance under this Plan would be sufficient to permit
                  a loan to be made in the amount of at least One Thousand
                  Dollars ($1,000) if the separate accounts were treated as a
                  single account;

                                    (ii) the Participant does not have any other
                  loan outstanding with respect to either his or her Aggregate
                  Account under this Plan or his or her account under the SIS
                  Plan;

                                    (iii) the loan is made during the period
                  beginning July 15, 1999, and ending on the SIS Plan
                  Affiliation Date; and

                                    (iv) the loan is made in compliance with all
                  provisions of this Section 6.3 except for the One Thousand
                  Dollar ($1,000) minimum amount requirement."

         3. The table of Predecessor Plans included in Appendix A shall be
amended to read in its entirety as follows:

<PAGE>   2

<TABLE>
<CAPTION>
         SCHEDULE                               PREDECESSOR PLAN                            PLAN AFFILIATION DATE
         --------                               ----------------                            ---------------------
<S>                          <C>                                                            <C>
         1                   Mid Maine Savings Bank, FSB 401(k) Savings Plan                January 1, 1996
         2                   Bank of New Hampshire  Corporation Tax Deferred Savings        July 1, 1996
                             & Investment Plan
         3                   SBERA 401(k) Plan As Adopted By Family  Mutual  Savings        April 1, 1997
                             Bank
         4                   Atlantic Bank 401(k) Profit Sharing Plan                       December 1, 1997
         5                   Concord Savings Bank 401(k) Plan                               November 1, 1998
         6                   CFX Corporation 401(k) Plan                                    December 15, 1998
         7                   SIS Bank Employees' Savings Incentive Plan                     December 31, 1999
</TABLE>

         4. The following Schedule 7 shall be added at the end of Appendix A:

                                 "SCHEDULE NO. 7
           RELATING TO THE SIS BANK EMPLOYEES' SAVINGS INCENTIVE PLAN

                  "The SIS Bank Employees' Savings Incentive Plan (the "SIS
         Plan") shall be merged into the Plan effective December 31, 1999. The
         provisions of the SIS Plan remaining in effect under this Plan with
         respect to the Predecessor Plan Account of a participant in the SIS
         Plan on December 30, 1999, shall be as set forth in the SIS Plan as in
         effect on such date, which is incorporated by reference herein; except
         that Section 8.5(c) of this Plan shall apply to the determination of
         the required beginning date for distribution of the Predecessor Plan
         Account for any Participant who attains age seventy and one half (70
         1/2) after December 31, 1998."

         5. This Fifth Amendment shall be effective as of January 1, 1999,
except as is otherwise specifically provided herein or may be required by
applicable law.

1.
         IN WITNESS WHEREOF, to record the adoption of this Fifth Amendment as
of the effective dates stated herein, Peoples Heritage Financial Group, Inc. has
caused this instrument to be executed by its duly authorized officer this 27th
day of August, 1999.

                                         PEOPLES HERITAGE FINANCIAL GROUP, INC.

                                         By /s/ Susan G. Shorey
                                         ---------------------------------------
                                         Its Vice President and Benefits Manager

                                       2

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00022-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00022-of-00352.parquet"}]]