Let me get this straight - you want to get rid of the 255 MP limit in WM?
I'm pretty sure you can insert MP costs of more than 255 into Wall Market, though it's uncertain whether it'll work or not. Playing with Libre suggested that, at the very least, setting the 'unused' MP byte to 1 would prevent those with less than 255MP using a skill.
But, you could just change character growth curves to pare down MP growth, and keep MP pools low. That way, you wouldn't actually need to exceed the 255 limit in the first place.