Install:

Using OpenIV, go to

C:\Program Files (x86)\Steam\steamapps\common\Grand Theft Auto V\x64e.rpf\levels\gta5\vehicles.rpf

and, in edit mode, open the "texture dictionary" file for the model you are using as a cvpi and replace skin/livery with the one from this download.

Vehicle model can be found here:

https://www.gta5-mods.com/vehicles/lapd-unmarked-cvpi