as with any aeg you can buy whole new gearboxes whole new upper recievers, batteries, all new bodies, give us a clue as to what you want to upgrade? it would make it easier to help you if you told us specifics. as to your stock swapping question it is going to cost you for a different stock..........IF you can find one, as i just looked a few places and didn't find anything remotely close even for a tm or nicer brand i'm thinking it would be easier to get a folding stock version. that's my $ .00