One approach would be to released the mod with a grid for a certain year with enough skins to fill a grid, preferentially the one the it's closer to the car the 3D model has been based off, and then release the skins for the remainder years as a separate download for those not needing so many skins.
Also, CM allows you to create preset grids with car+skin selections via .cmpreset files (p.e., one grid per year). But these would have to be dropped on its appdata folder (AppData\Local\AcTools Content Manager\Presets\Race Grids), and sometimes end-users struggle to do the simplest things. Might need some direct editing on the resulting file so not to enforce some undesired extra settings, though.