Your first quest is to find out what the plane is presently covered with. If you use a different covering, the color won't match.

Next, if it's Ultracote, Ultracote has a nice paper backing that you can draw your designs on before cutting (Don't forget to draw a mirror image) - You will still have to cut by hand, but having lines makes it easier (You can use sharp sizzors too). The bad news is, trim solvent doesn't work on UC

If it's MK, you CAN use trim solvent, but you'll have to make templates to get the cuts right