This is not possible for copyright reasons alone. Anyone who uploads something to CC is also the responsible author. Downloading is allowed, but changing it is not. On the one hand, you would have to ask the author for every planned change whether you can change something. On the other hand that would also be unfair to the person who has invested many hours and whose work would then simply be changed. Some people take a more relaxed view of this and some don't. Either you make the livery you want yourself and plan a certain amount of time for it, or you take what is offered. Or you use Photoshop and the TSW editor to create a complete texture yourself, including spec, normal, metallic maps and decals.
