I don’t really talk here much, but I figured I should mentioned something a rather underrated game I’ve discovered called “Wildermyth”. It’s a sort of turn based RPG, but all the character and enemy tokens are sort of like cardboard cutouts. It peaked my curiosity, because it recently got modding potential, and, because of how the sprites for characters don’t move much at all, it could be an easy game to create a fat mod for?
If you are curious about it, I found it on steam, currently on sale for 20 USD until June 22nd, 2021.
The main thing that that varies on is the engine. From googling I couldn’t find which engine is it.
If it is a common engine, unity, unreal, game maker, godot, etc, then replacement mods would be straight forward enough. These could just replace the graphics of the game.
Something like adding a fat mechanic is probably out of the question unless the devs allow mod support. Another means of mod support is config files. If the game has files that define stats, you can edit those for major changes. Usually even then adding new stuff is hard.
So, if you want to pursue this, first find out the engine and find the modding tools for it.
If it is proprietary, look through the game files and see what you can open. Many files that look unopenable could be text or zip.