Last post before I go offline~
If you understand this, you need to change it's data on Section B, 0x40-0x41 to 0x004C.
I've worked on it and I find that no matter what you do, although in game it will show up as the ??? Arceus, when you enter a battle with it, it automatically transforms back to it's normal form.
The below Arceus is the first one I made~
(Quoted from my post in the PokemonGTS forums, lol~)
I'll post pics later of how to use the Hex Editor, if no one has posted yet later~