Is it possible to insert dummy cars with a specified skin? I want to make a screenshot with all of my skins but idk how I would do that properly.

Launch local network host from one client,open as many clients as you need and join that host.

Or you can set a new start point using Layout editor and spawning AI cars with your skins. Do not forget to set a new start point each time you spawn a car and do not forget to pause the game so that AI do not drive away.

Thanks guys I'll try this stuff out.