Depends greatly on if it is going on a higher altitude pressurized aircraft for one. If so, you cannot just put whatever you feel is appropriate. There are very specific materials for those that you cannot just buy from Fellers, etc like 3M A7322 and A7706. On those the aircraft logs have to be notated, inspected, exact weight and composition of the materials, location, specific certifications for the installers, etc.
Google those 3M numbers above and read the data sheets for them to give you and idea of requirements....
Things like "The sale of exterior aircraft graphic film is restricted to qualified parties.", "Usually an engineering change request procedure must be engaged and completed prior to proceeding with the approved process to apply graphic film onto aircrafts."
On smaller low flying aircraft it is much more relaxed but still many things have to be considered. Cannot just take a torch to rivets, cannot just make cuts on the plane, must be aware that what might look like a tiny pinhole in the fuselage might be an important sensor or something. They are also extremely thin and easy to dent. We have done stuff on a number of smaller planes and helicopters but nothing on anything that has a pressurized cabin.