I will share another quick tip I use quite often for touching up. A regular old Q Tip works great. I used them also with rattle can paints. I will spray into the cap, then use a Q Tip to dab out the scratches, and toss it when I am done.
For really fine touch ups, I've also used match ends (not the side with the sulfer) and tooth picks.
Oh yeah, don't forget to always invert rattle can paints upside down and spray until only air escapes. This will clean out the paint from the nozzle and stops clogged up tips.