That is why international treaties come with implicit or explicit enforcement options

That is not how international law works, you don't get to say "we are a new country and therefore not bound by treaties that earlier forms did."

This principle was established when Nazis were convicted for war crimes at Nuremburg for violating treaties that their predecessor state the Weimar Republic signed, even after the Nazi's repudiated those treaties and claimed they were signed by an illegitimate state, and that they were a new Reich, not like the Wiemar Republic.

Basically if territory changes hand to an existing state that state will obviously still have obligations, and if a new state is formed, then generally it is assumed to still carry the obligations of the previous state. There is no "one weird trick" to avoid international law. I assure you that the diplomats and lawyers 80 years ago thought of these possibilities. They saw what resulted from the Soviet and Nazi mutual POW slaughters, and set up international law so no one could ignore it.