When you said open slather I thought you were talking about the lights fitted to cars on the roads in NZ Hotwire.. I see all sorts of crap when I am driving around town, blacked out lights, blue headlights, red heahlights, bongo vans lit up like Christmas trees, etc. Just buy any old cheap sh*t of TradeMe and slap it on your car, don't worry about the rules. Probably all still get a WoF though..
Back the original post, I can't see anything immediately obvious to make the lights illegal, the blacked out backing is legal from the factory I think so you should be Ok, used to need to be made to meet certain standards. Your average WoF inspector would probably not notice as long as they are correctly aligned and have the right beam pattern.