I apologize for the bump, but how hasn't this gotten more attention? And I see talk about expanding the level cap further than 255?!?! I assume you'd need to do some serious changes to the code for that one correct?
255 is a maximum value one byte can have. Whenever a lvl appears in the pokemon gba memory it's treated as one byte. To change that, you'd need to modify a TON of opcodes to correctly read and write levels.
Why would you want to go further than 255 tho? Seems like an overkill to me.