Turn off livery on modded police cars

[epoqx]

So, I'm working a lot on the dispatch.meta recently, and right now I'm trying to make a dispatch of undercover FBI peds. I found the peds, but I'm having troubles to find the cars.
Except reworked vanilla cars transformed to unmarked, there doesn't seem to be a lot non-ELS that are working properly.
I don't use ELS because it doesn't seem to be usefull for the AI in single player mod without LSPDFR.
Most of the amazing modded, non-ELS cars are marked.

• Is it possible to take off the livery so I can use the basic color pattern of a car while keeping the police lights ? (Making it an unmarked/undercover car)
• If not, can ELS for a non-LSPDFR user be usefull ? (Dispatched/Spawned from popgroup law vehicles can use it ?)

Thanks !