All treaties, settlements and borders are subject to be changed. It's simply a fact.
It is entirely possible that, in a war or as a settlement, or under pressure, or by sale/trade, or by volunteer Russia will give the Kurils to Japan, or the United States will revise its position on Taiwan or Hong Kong (you've already see a Trump Administration send the signal he's willing to do this).
These relations are complicated, as various decisions made by different sovereignties will be replied to, can spoil relationships, can spoil trust, etc.
A nation can also ruin its reputation by being 'too flippant' in recognizing territory until its not convenient to do so any more. There's a giant fuzzy 'you-have-to-be-able-to-tell-the-future' calculus that is done in simulating various choices on how to proceed with sovereign decisions, as effects can be quite wide ranging.
America flipping its opinion on the sovereignty of the former British colony Hong Kong or on the civil war safehaven Taiwan, would represent a huge and damaging departure in relations with China. The United States may do such a thing, but would only do it if the 'realpolitik' calculus allowed it to risk - or wanted it to aggress - a war.
There's never a simple thing in geopolitics. We can only look to history, to policies and treaties and to potential outcomes to explain and predict. The United States breaking with long standing treaties would be huge news in this regard.