What does this mean for the mod itself? Well, ISO patching is significantly trickier than altering the PC version, because file sizes must remain the same. Those who have tried their hand at cartridge game modding will likely have an idea what I'm talking about. Because we don't have the tools to rebuild a playable CD from the constituent files, we have to maintain the data structures established when the game was first printed. This means that no file can exceed the size of the original.
There are, however, ways around this. The game data is identical on each disc - only the cutscenes vary - so there's a great deal of redundant text and info on each. There are details of enemies and weapons, for instance, that could only be encountered on disc two, available on disc one. By excising this text, we can free up a little more space to work with, which is important when rewriting the enemy AI (where space simply *can't* be compromised).