I learned a nice trick from a friend of mine.. He suggested using a DA and 320 grit paper...put it on the head of the run and spin it until you sand it down to the other clear level as Brian has pointed out... I like the razor, but you gotta be super careful as Bob suggested too. If you are not careful with a razor blade you will pop the head of the run off all the way down to the base... Dry time and being able to read the paint are very important.
Just thought I would throw my 2 cents in
BTW the DA trick is my new favorite... I tried it out on something someone ran the crap out of, and it saved him having to clear it again... Paint was the flattest thing out of my garage this year, and I didn't even paint it