Sooo essentially you are saying there is no modding this game?
either that, or it may be way to tedious, and only doable with harmony or some other bepinex'ing. I may know a thing or two in programming, but from my experience people turn to BepInEx usually if the game is not mono (as in Assemblysharp/firstpass are not accessible)
MAAAYYYBE some internal logic is hidden in those animation plugins the dev used, but, again, i couldn't find anything worth editing.
though maybe[2] you could try to decompile the game completely, instead of digging through dlls, but its out of my scope. (at least for the foreseeable future)