- Oct 30, 2017
That's a question that will require a surprisingly nuanced answer.
The biggest thing that a C source, or even a disassembly, brings over standard ROM hacking is flexibility. If you want to create some Kaze-level super hack with crazy custom mechanics and with new enemies and with big modifications of the engine, and so on, doing it with this code will be far easier. If you just want to replace some levels with your own custom ones, there's already a large number of good tools that work fine (console compatibility aside) with just the standard ROM. Since no tooling exists for this code leak, doing things like that will be harder until people have time to create the tooling.
Once the tooling's there, which could take a while, using the C code will make anything above a super-trivial ROM hack far easier.
edit: also, having the source code will make it far easier to document and understand the game. The knowledge gained from that documentation may or may not be relevant to any given mod someone decides to do. SM64 is already one of the most examined games (see any panen video or kaze hack), so there is already a good amount known about this game.