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.
Dwarf Fortress is like this too, in fact much of the game can be modded from such files. I like that, but I do understand the frustrations of the developer who not only saw their games cracked but also trained back in the day. It presaged what was to come heh.