Funny this question has popped up, I'm looking in to this myself, the easy thing to notice with your request however... You're speaking about a game that was created using Rpg Maker 2k3, which has been edited and such, by himself (or whoever), but PE, is created based on the games (which only uses 4 moves max), unfortunately for you, you will need scripting knowledge (vastly), to understand what to edit, mainly since all the scripts that need editing are like 0..4 and moves etc. It's these that make the moves fixed to 4, however, there's more to it than that, you'll probably have to look in to HM/TM's, CPU Pokémon and so forth... But good news is, if you can figure this out, you're on for a winner... Bad news... Once you've figured out that, you've then got the nice problem of showing all these extra moves in battle (if you haven't changed the layout of the battle that is), it seems more of a long job than a hard job to me, but definitely possible.
Try looking for anything in PokeBattle_Battle that uses 0..4 or something similar that checks moves immediately after.
