Kind of how they patch that out, but instead just patching out instructions. Difficult to describe.... X86 copy to ARM copy instructions, replace the instruction, but memory management would get insane....
@SylverReZ, also iirc mame didnt emulate donkey kong's sound correctly and thats why billy mitchell's gameplay in that king of kong documentary has no sound
@Psionic Roshambo, CPS II machines were also difficult due to the suicide battery keeping the chips alive containing the decryption keys to decrypt the game. And if the battery died, then the game won't boot.