I've installed a Lamborghini Reventon cop car into the pstockade model due to it not being used in game except in 1 mission (and LCPDFR.) Basically, I want to add another livery to the car. I know that you need to add "+livery" to vehicles.ide but the pstockade does not normally support more than 1 livery (I may be wrong.) I was wondering whether there is a way to have more than one livery?

 

Link to car if you need it: http://www.gta4-mods.com/vehicles/lamborghini-reventon-police-nfs-hot-pursuit-e-f9082

If the car model, which you installed, supports multiple liveries, you may replace those that already are there with, for example, SparkIV, selecting .wtd file in vehicles.img via Spark, and pressing "edit' button. If the model supports only one livery, there's no way to make a difference. 

The +livery thing is all you need to make it multi-livery. You may however need to edit a number in your trainer.ini to make it work with the trainer.

The livery support depends on two things - the model itself and the +livery line in vehicles.ide.