Hell, let's imagine the United States ceding Maine to Canada without the input of anybody within Maine. Once the treaty is signed, they're told to relocate. Yeah...I don't see that playing well, and that's from one democratic state to another.
You don't need to imagine it, the UK and US have already done that with Diego Gracia. The UK gave the island to the US to use and booted off the inhabitants, which the US seems fine with since they get a nice big military base in the Indian Ocean.
The inhabitants have tried to get their island through the courts, but haven't succeeded. The UK was even exposed as trying to make it impossible for them to ever
get their island back off the US.
Even after the peace treaty was signed, the Cardassian time and again would attack Federation targets whenever there was an advantage to be had. TNG's "The Chase" and DS9's "Emissary" are perfect examples.
These were both before the treaty was signed.