<PAGE>   1
                                                                  EXHIBIT 10.39

                                AMENDMENT TO THE
               GENUINE PARTS COMPANY SUPPLEMENTAL RETIREMENT PLAN

         This Amendment ("Amendment") to the Genuine Parts Company Supplemental
Retirement Plan (the "Plan") is made and executed this 19 day of April, 1999,
to be effective as of the date hereof.

         WHEREAS, the Compensation and Stock Option Committee of the Board of
Directors of Genuine Parts Company (the "Company") has approved an amendment to
the Plan pursuant to Section 6.08 of the Plan, to change the definition of
"Change of Control" for purposes of the Plan;

         NOW, THEREFORE, in accordance with Section 6.08 of the Plan, the Plan
is hereby amended as follows:

         1. CHANGE OF CONTROL DEFINITION. The current Section 5.01(c) of the
Plan is hereby deleted in its entirety and the following is substituted
therefor:

                  A Change of Control of Genuine Parts means and includes each
         of the following:

                  (1) The acquisition by any individual, entity or group
         (within the meaning of Section 13(d)(3) or 14(d)(2) of the 1934 Act)
         (a "Person") of beneficial ownership (within the meaning of Rule 13d-3
         promulgated under the 1934 Act) of 20% or more of the combined voting
         power of the then outstanding voting securities of Genuine Parts
         entitled to vote generally in the election of directors (the
         "Outstanding Company Voting Securities"); provided, however, that for
         purposes of this subsection (1), the following acquisitions shall not
         constitute a Change of Control: (i) any acquisition by a Person who is
         on May 1, 1999 the beneficial owner of 20% or more of the Outstanding
         Company Voting Securities, (ii) any acquisition directly from Genuine
         Parts, (iii) any acquisition by Genuine Parts, (iv) any acquisition by
         any employee benefit plan (or related trust) sponsored or maintained
         by Genuine Parts or any corporation controlled by Genuine Parts, or
         (v) any acquisition by any corporation pursuant to a transaction which
         complies with clauses (i), (ii) and (iii) of subsection (3) of this
         definition; or

                  (2) Individuals who, as of May 1, 1999, constitute the Board
         (the "Incumbent Board") cease for any reason to constitute at least a
         majority of the Board; provided, however, that any individual becoming
         a director subsequent to May 1, 1999 whose election, or nomination for
         election by Genuine Parts' shareholders, was approved by a vote of at
         least a majority of the directors then comprising the Incumbent Board
         shall be considered as though such individual were a member of the
         Incumbent Board, but excluding, for this purpose, any such individual
         whose initial assumption of office occurs as a result of an actual or
         threatened election contest with respect to the election or removal of
         directors or



<PAGE>   2


         other actual or threatened solicitation of proxies or consents by or
         on behalf of a Person other than the Board; or

                  (3) Consummation of a reorganization, merger, consolidation
         or share exchange or sale or other disposition of all or substantially
         all of the assets of Genuine Parts (a "Business Combination"), in each
         case, unless, following such Business Combination, (i) all or
         substantially all of the individuals and entities who were the
         beneficial owners of the Outstanding Company Voting Securities
         immediately prior to such Business Combination beneficially own,
         directly or indirectly, more than 50% of the combined voting power of
         the then outstanding voting securities entitled to vote generally in
         the election of directors of the corporation resulting from such
         Business Combination (including, without limitation, a corporation
         which as a result of such transaction owns Genuine Parts or all or
         substantially all of Genuine Parts' assets either directly or through
         one or more subsidiaries) in substantially the same proportions as
         their ownership, immediately prior to such Business Combination of the
         Outstanding Company Voting Securities, and (ii) no Person (excluding
         any corporation resulting from such Business Combination or any
         employee benefit plan (or related trust) of Genuine Parts or such
         corporation resulting from such Business Combination) beneficially
         owns, directly or indirectly, 20% or more of the combined voting power
         of the then outstanding voting securities of such corporation except
         to the extent that such ownership existed prior to the Business
         Combination, and (iii) at least a majority of the members of the board
         of directors of the corporation resulting from such Business
         Combination were members of the Incumbent Board at the time of the
         execution of the initial agreement, or of the action of the Board,
         providing for such Business Combination; or

                  (4) Approval by the shareholders of Genuine Parts of a
         complete liquidation or dissolution of Genuine Parts.

         2. EFFECT OF AMENDMENT. As modified hereby, the provisions of the
Plan, as heretofore amended, shall remain in full force and effect, and the
Plan may be restated, as amended hereby, in its entirety.

         IN WITNESS WHEREOF, the Company has caused this Amendment to be duly
executed as of the date first above written.



                                        GENUINE PARTS COMPANY

                                        By: /s/ George W. Kalafut
                                            -----------------------------------
                                        Name: George W. Kalafut
                                              ---------------------------------
                                        Title: Exec Vice-President Finance &
                                               Adminstration
                                               --------------------------------


                                     - 2 -