I am against city cultural flip because of enormous gameplay frustration/exploitability, and border cultural changes because of lack of realism.
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Probably yes, but it'd be rare cases of limited scale ethnic divisions (and I'd say government almost always used coercion in such situations), and we are talking about all empires of the world being able to casually take territory of all other alien empires not with military or diplomacy but, uhm, citizens (???) and that happening all the time across history.
Okay I can imagine Ucrainian city flipping to Russia, for example

but that's one of very rare instances when such mechanic would make sense.