Yes you can re-clear a car to add durability. With many paints it'll give it a deeper look once cut and buffed.
Wet sand w/ 400 and 600 grit (may be able to get away with only 600 to keep the MIL thickness up)reprep, mask and spray away. Personally I might mix it a bit "hotter" so it bites into the existing clear better...kind of like a blending mix of clearcoat.
