I did some testing and here is what I found. I laid down some future of a piece of plastic that is used in all the stores. It is pliable but stiff and since I will be painting over the future, I don't think it mattered. I then made to "lines" bordered one by Tamiya tape and one by Scotch Blue. I then sprayed Vallejo acrylic polyurethane primer on one section, hand painted some Vallejo light grey over another section, and lastly hand painted some Vallejo dark grey over another.
Took two coats to cover with the light grey as it wanted to "pool" towards the tape. I had things pretty flat I think. The dark grey was pretty good after one coat. I then sprayed some RLM 66 over the primer. 24 hours to cure and then I lifted up the tape without using a blade to score it. Both lines were almost perfect, but the Tamiya tape was slightly better if you get real close or use a small magnifier.
I then took an old 1/72 FW-190 canopy and repeated it with the primer and the RLM 66 after masking the canopy but NO future was used. Good lines, but a little ragged on some of the smaller lines but not really noticeable unless you are a perfectionist. the primer was brushed on and it ran away from the plastic. Then back over it more with some dabbing of the brush and it all held. 24 hours later the primer held and leveled really well.
So I guess it will work, it just takes some patience with either a brush or an airbrush and any combination.
John