consider this too,
contracts do not change year to year without consent of the parties. Divorce law changes every year along with child support formulas.
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Yes, and the legal system is usually very loathe to intervene and rewrite contracts. They may pronounce some type of clause as void and unenforceable, which can affect existing contracts, but those are usually exceptional cases where the clause was in violation of existing laws in the first place.
With divorce, and the family courts, there is no hesitation to alter the agreement midstream. That’s probably because the courts know very well they aren’t dealing with a contract. All those family court judges are lawyers, after all, and so if a layman like me knows these facts about contracts, they must all know these facts as well. You can’t pass a Bar exam anywhere in the country without passing a test on contract law.