Try not to get it in the pad area. Use electrical tape to tape off the contact area. The pads will wear the paint off, but it won't be a smooth transition. When i painted my 13" rotors, i did the entire rotor. When the pads wore it away, the edge was jagged. I had to redo them by taping off the swept area.
The pic on the left was done by spraying the entire rotor with no taping. The pic on the right was done masking off the swept area with electrical tape (easy to curve)
It's been 3 weeks and they still look great