Well this is simple i hope someone has an answer.

Well i have some mods installed, and if i look in the textures file i can see more than 1 skin, there's 3 to be exact. But if i go in-game , the cop cars only spawn with the first one. I tried with a Trainer to change the skin but i was only able to change the color.

So, how do i change to the others skins (if possible).

add +livery in the vehicle.ide at the end of the car line. that should make it. if you're using simple native trainer there is an option to change the livery.

Mmm, thanks! I will try this now.