Really dont think its restricted mate, on paper it makes 13 BHP so unless youve got a full license you cant do much to it. also any performance mods will probably only add a few horses for a lot of cash. also there arent many mods for these at all youll have to graft and adjust parts to fit so id leave it :(.
If your still desperate to modify it i can help you message me at: Kingdeeley@hotmail.com ive had experience tuning 4 stroke 125´s before.