A contract is a contract--both parties are bound by its terms. While either party is free to *ask* the other one to change it, neither party may require the other one to make any changes to an already-executed contract, or unilaterally make any changes to the contract. Or rather: if the contract itself provides  that one party may make certain changes or require certain additional things of the other party, then that party may do so, but only to the extent the contract specifically permits. Therefore, unless the contract gives the former owner the right to make some changes or impose additional terms, you are under no obligation to do anything other than what is set out in the contract. It'd be a good idea to review the contract again, to double check what it's terms were.