In fact you can paint any decal film, as long as you get good coverage. For stuff like canopy lines I often use old roundrels, etc.
The sign painters that work on my stuff use the base coat on first technique. In fact if they're putting graphics on concrete like numbers on steps at a stadium, they mix up a batch of the right grey first.
But don't forget, to get straight and parallel edges for lines that are too narrow for Gerald's nifty tool, paint the stripe color first, mask it with a tape strip, shoot on a little more stripe color, then the surrounding color. I always do wing walk lines that way, it's pretty easy.