I downloaded this model as linked above, and since its an add-on I had to do some configuring to add it as an emergency vehicle with the rest of the roster. I'm now able to select it from the police garage, use it as a stand-in for NOOSE Riot, etc, but I wasn't able to pull people over in it because it wasn't classed as an emergency vehicle.
So I went to the vehicles.meta and added FLAG_LAW_ENFORCEMENT FLAG_EMERGENCY_SERVICE, and that enabled me to perform as a true police vehicle. However, the in-game name shows as "(blank), emergency", when it should be showing as "Mrap, Emergency". I tried removing FLAG_AVERAGE_CAR, and that did nothing, so now I'm out of ideas.