The principle of the sanctity of contracts, applied mutatis mutandis to international agreements, is known as

The sanctity of contracts applied to international agreements is pacta sunt servanda: every treaty in force binds the parties and must be performed by them in good faith (Article 26, Vienna Convention on the Law of Treaties, 1969). Rebus sic stantibus is the exception for a fundamental change of circumstances, and jus cogens means peremptory norms from which no derogation is permitted, so a named principle does fit and the catch-all is wrong.