You will be fine powercoating them, but you will have to take them to a decent wheel place. They will PC the wheel first, then diamond turn/cut the lip again, before laquering the whole wheel and baking it on. That way you dont need to mask it. Wont be able to use a cheap wheen place though, will likely have to send them away to someone decent, like Spit and Polish or Lepsons.
IIRC my old Rotas got sent to Lepsons (via MyAlloys in Basingstoke) to be done when I needed the polished lip, and thats exactly what they did to it. Beleive me you will see the difference they make doing it properly, the laquer was about half an inch thick on them and pretty indestructable! Way better than OEM! Infact Lepsons and Spit and Polish look like they may be down the road for you, thats good luck!