As soon as you are on top, your behaviour might change.
It might, it might not. America’s behavior didn’t change; from the start they’ve been aggressive and expansionist, the scope just grew as they became more powerful.
China’s been growing rapidly for decades while very seldomly acting militarily outside their borders. They don’t seem to have expansionist goals outside those declared over 70 years ago (ie Taiwan) and have even negotiated down on border conflicts. It’s not impossible but it’d be strange for China to make a complete about-turn on their stated policy of non-intervention.
Tibet was recognised by every country on the planet as sovereign Chinese territory, both then and today.
(That was also like 70 years ago, China’s last war was against Vietnam in the late 1970s)