The assumption of personal liability where none before existed,1 or a waiver of a right of a subcontractor to complete the contract himself or to hire someone other than the chief contractor to complete it.2 is a consideration for a modification. Payment by one party in advance of the time at which it is due under the original contract, is consideration for a modification of the original contract reducing the amount to be paid under the original contract.3 If both parties agree to an extension of time for the performance of the contract, the promise of one to grant such an extension is consideration for the promise of the other to grant such extension.4 If a party who is originally jointly liable upon a contract has been released therefrom, a subsequent contract by which the party who was originally released is to become liable again upon such contract, is consideration for a promise to release the other original joint party thereto.5