Afaik dlss and fsr are pretrained models and they don’t train them for each specific game.
Maybe I misunderstood it and its not about adjustment training to specific games, and its about adjusting settings or something like that. I searched for a resource to point to that, but cannot find. It's really hard to search about this topic online, because its always the same basic explanations what Ai upsaclers are (probably written by an Ai model itself...).
Modders totally do enable them for games that don’t support them natively
I know of modders being able to replace an existing model that already has motion vectors and depth. It would just reuse those information, because the API is agnostic to the models. If modders add vectors and depth by their own, that does not change the fact that DLSS or FSR 2+ can only work with those data.