Last time I painted a serious airplane (2006...) Phil Granderson gave me a great bit of advice. Mr Clean "Magic Eraser" pads are AMAZING for cleaning up pencil lines, light overspray and generally brightening up your paint job while you are working on it. Phil credits the lovely Kathleen, but I doubt that Kathleen has spent a lot of time erasing pencil lines from model airplanes.
The best thing about it is that it is so soft and takes such little pressure, that there is nearly no chance of damaging anything in the attempt. The one to use is the original, non-scented Magic Eraser, and use just water to dampen it and squeeze it out, then just rub the offending area. It will conform and clean a pencil line right up to the paint edge. Also, very light overspray. When it starts turning colors, rinse it out, and go again. It will abrade away pretty quickly, then get a new one.
Brett