How can i add light bars to a vehicle of my choice?

Im new. Ill start with that. I want to be able to choose which cars go in my department leo fleets. So how can i put lightbars and lights on on any car i choose? Say i see a mclaren and i want it to be an LEO car with lightbars etc. Can i? how do i go about doing that if so? Or do i actually need to randomly find the maker of the car model to give me his code etc? Please use good detail if answering since im not that experienced.
Thanks

You can either use z3d editor or use a simple script like this one, which is easy to use and can be done in game