Modding Decals?

Hey all, I'm a lurker here but I was wondering about a mod diea. There are a fair few decals in RL that I'm not overly keen on. I've got a few great ideas for decals and skins for cars that I'd love to work and I don't think there wouldn't be any modelling needed, just flat texture creation.

Is this possible to do? Or is it more deceptive than first glance. I can imagine that the way decals are coloured would maybe cause issues, the texture for the decals being mapped may have to have special properties or one for each colour?

If anyone can shed some light on this as I'd be super willing to make custom decals. Thanks for your time.