82 main jet is what you need for a derestricted a50, anything bigger wont make it go better but it may run worse.
An open filter is like a foam filter or a k&n type filter, you will have to rejet up if fitting one of these. Far as i knew all a50's came with an 80 main jet
Also cutting the cdi shouldnt kill the scoot, mine is cut and i did 10,000 km on it last yr with no real probs. Got 23,500-24,000 km on it now i think.