You really can just request an entry point, one needs to be found in a game to work. It takes a lot of work and time to find an exploit, then more time and work to code some way to exploit that entry point.
Now of course since Majora's Mask uses the same engine as OoT, I can see where one would wonder if the same exploit was in that game as well. And the answer is, most likely not. Nintendo would have ensure that would be patched before the release or with an update after the OoT exploit was found.