First, thank you very much for your comment @BarryBL
My intention was to show a way, how you maybe can implement custom liveries on xbox/ps/pc without modifying game datas. I am not a game developer so i'm not sure if it works the way i think, but is my idea different to the way, how new liveries coming to the game with DLCs? The 3d-model for all multiplayer cars is the same, only the livery is different. So if there's a possibility to paint a custom livery on a pc and download it from your servers in-game, i think, it's modifiying without a change of game data from the user site.
I hope you know what i mean.
Thank you very much for your time.
Many greetings.