Vits12h ago(Edited 12h ago)
That first “case” is not what we are talking about here.
According to the article, the system apparently marks different versions of the game as a Switch 2 version. This means it is not just like putting a PS4 game into a PS5 and having it run at a more stable frame rate simply because the hardware can handle it.
What this mark probably means is that the game has been made “upgradable” for the Switch 2 or what you are calling “going as far as to rewrite the code to take advantage.” If you have ever messed around with a modded Switch or PS4, you know that no code is being rewritten, it is pretty much just sliding a slider.