Depends. In some games it is extremely easy (like textures and such for Minecraft Story Mode) where in others, it can be extremely difficult (personal models going over character models, animations, etc.)
4
Anonymous#12w
Is it more of like an art type thing or more coding and software development stuff? Or both?
1
AnonymousOP2w
Model replacements are very code heavy cause you usually gotta set specific numbers to the bones of the models and animations. If textures, a lot of the time there is a program that lets you extract and edit pngs and patch it into the game