Relatively recently, CM got a feature allowing to quickly edit skins. It’s still not really finished , but now, at least, description of editable textures is not hard-coded. Now we need to add full support for all cars, this GitHub will be used to put work of everybody together. To contribute to this project there is some rules to follow.
To learn how to create paint shop files for cars you can look at examples located in C:\Users\%USERPROFILE%\AppData\Local\AcTools Content Manager\Data\Paint Shop or look at the Content Manager Website. To see released cars you can look at this Google Sheet
Currently priority goes to Kunos Cars that need to be added to the Kunos.json file (Please move it to 'Data (User)' before editing it). If you want to use textures put them in Kunos Folder and then in car name folder, as example for the Ferrari 488 GTB you should create a folder named ks_ferrari_488_gtb in the Kunos folder and then put all textures in it, for calipers AO path should look like ./ks_ferrari_488_gtb/calipers_ao.png.