I decided to mess around with some visual settings in the game to match the vanilla emergency vehicles with the ELS emissives, and found setting the siren coronas to 0.00 did the trick, now the vanilla cars look the same as ELS cars with lights activated from a distance and no more corona bloom.

 

However, in doing this, the rotator style lights no longer light up since they have no coronas. I've been replacing the vanilla vehicles with other vanilla style vehicles that have LED lights instead. The issue I'm running into is sometimes the Police and Sheriff vehicles spawn with the older rotator style lights instead of the LEDs, and they obviously don't light up. I've tried messing with the vehicles.meta settings and the EXTRAS options, however the Sheriff car still spawns with the older rotator AND the LED.

 

How can I prevent the Police and Sheriff vehicles from spawning with the rotator lights, which is extra 2?

editing vehiclemodelsets.meta might be helpful. Don't know whether it will work so I suggest making a backup before you make the edit.
The reason why I think vehiclemodelsets.meta might help is because it include edit on things like extra1-10. Hope this work for you.