First rule is if you can pull it off, pull it off.
I guess by rear centre reflector you mean the clear thing that goes across the back of the boot.
Best way to paint it is to remove it from the car, clean it thoroughly with prepwash or prepsol (avaliable from auto retailers) then paint it with some proper PLASTIC or FLEXABLE paint primer, followed by some FLEXABLE or PLASTIC paint. Dont just use normal paint, it will flake off over time.
You can either buy the paint / primer in a spraycan, or if you have compressor equipment use a proper spraygun. The latter is best.
Remember to clean the spraying area thoroughly so its free of dust and crud that may land in your paint as a result of the turbulence generated by the spraying action.
Any more questions you have, just post again.