By later times it seems this was tougher, I remember trying it with Ultima IX and utterly failing to locate a single relevant memory location after a solid week.
Ya especially with DRM or multiplayer lockdown measures.
But there is still a revolution where most game files are JSON or plain text (like that build list from Star Trek Armada 2).
Not sure what game's save file it was, but I remember learning about big vs little endian this way. And before that, why I would suddenly get negative money if I made it too big!