Cool idea but....
The DA didn't do his research very well, is my first impression. If you believe the vehicle is a police vehicle, then you believe the operator is a police officer. Over here you cannot have displayed a blue light, even if it's turned off.
The local police would not tolerate it anyway. The first time he drives past a crime or accident scene and does not stop to render assistance, the complaint calls would flood the police switchboard.
I do know people who do this sort of thing. They mask all the police identifying features, until they get to the car show or whatever. Then once on private property, they reveal all. Can look awesome.