Bonneville lights won't work that way. The new ricer or euopean lights have smaller round reflector assemblies. You can paint the other areas without affecting the light. Our lights use the whole chamber face to project the light. Your reflector is the same size as the frontal surface area of the headlight.
The majority of the projected light actually comes from the outer fringes of the reflector assembly, and the least from the center where the lamp is. If you mask these off, you'll kill a higher percentage of light than the area you mask off. You will
ALSO probably get a ticket, your lights will look like **** after the winter from abuse, and the new headlights will kill your pocketbook.
Go with headlight covers. BonnieAlien, Terminator, Allmachtige are all running them. They look really good.