There are not any differents about materials. For cop livery, CARSKIN shader also works for cop car.
These meshes are common for race and police cars:
Other parts works by add damage0 and damage1 names, before their parts names, like: KIT00-DAMAGE0-BODY-A and KIT00-DAMAGE1-FRONT-WINDOW-A. Remember, All parts must have damage0 and damage1.
These mount points use for cop cars: (For their cop lights)
Converting race cars is as easy as police cars, so you can do it! ;)