In a land contract, the court will grant specific performance as a matter of course if the contract is otherwise unobjectionable. Courts don't inquire into the adequacy of consideration. Black Industries v. Bush . Alaska Packers . A modification made to meet unforeseen changes in circumstances operates as partial rescission, and is enforceable.
Good faith is required in contract modifications.
Austin v. Loral . For a sale of goods under the UCC, a modification requires only good faith, no consideration required. A contract is voidable on the ground of duress when it is established that the party making the claim was forced to agree to it by means of a wrongful threat precluding the exercise of free will. A Full Payment Check will discharge a debt when the receiving party has notice of the terms upon which he accepts it. Kibler v. Garrett .