Vinyls are a great customizable cosmetic for a vehicle but when it comes down to choices of vinyls to pick, customization to vinyls already in the game can be edited with graphic editors to create or import unique vinyls.
Graphic editing software
Hex editing software
Designing the vinyl
Get the required editors to modify a vinyl.
Extract a vehicle texture that goes to the corresponding vinyl, then open it up in a photo editor which you'll be adding separate layers for each RGB layer to design. Each color assigns the design to a specific color of the paint kits. Red is the first color, Green goes to the second and the last one is Blue.
When you're finished, export your vinyl to DDS with RGBA format, mipmaps generated and no compression. The resulting size should end up with 21.3MB and to successfully replace the vinyl, open the dds in a hex editor to fill the end with 0 since each sp2 skins are 0x1555600 bytes long. After that, rename your vinyl and extension like this "(character_you're_replacing_vinyl_for)_skin(skinnumber).gpu.sp2" (example: sonic_skin12.gpu.sp2) and test it on the vinyl you've replaced. Vinyls go into "localcharacters\charactername\skins\".
Out of all skins, Blaze is the the only character to have the default vinyl.
If you're importing a vinyl from another game, edit the vinyl to fit the vehicle and test it in the garage until you get the correct results.