1,2,3: I understand, thank you for the quick response
I just have one more question which would be better asked as an example:
I have a Arcanine which I want to mega evolve in-game. To do so, I replaced the model of Shaymin with a custom mega model of Arcanine. Using pk3DS, can I make Arcanine mega evolve to Shaymin so that it displays the custom model or do I have to include an alternate form for Arcanine using another method?