If you're intending to imply that the British didn't need to hand over Hong Kong because China changed rulers, I'm afraid that's not really how the law works. And, in any case, the negotiation of 1984 (https://en.wikipedia.org/wiki/Sino-British_Joint_Declaration) between Britain and the PRC set up Hong Kong to become a PRC territory in 1997.

That's not quite the equivalence. This is more like you having a piece of paper from the old owner of a property showing that you're entitled to passage and showing it to the new owner.

The point is that no matter how many laws get passed, you could very easily see yourself as from Hong Kong, not China, and you shouldn't get death threats for saying as such.

This is totally separate from the point you were making. You can say you're from Hong Kong, but it's part of China. That you shouldn't get death threats should go without saying.