It's all 65c816 machine code, which is well documented. You'd run the ROM through a disassembler and use an emulator to find out what everything does. Most (all

It's all 65c816 machine code, which is well documented. You'd run the ROM through a disassembler and use an emulator to find out what everything does. Most (all?) of the disassembly work has already been done though, as SMW is very, very popular to romhack.