Here's the scenario..
You crash, either by hitting someone, or them hitting you. Your insurance assesses your car and finds it is modified. You didn't tell them, they void your insurance. You will need to pay for the repairs on your car, and any third party bill.
Not too bad, a bumper for the car you hit, not particularly expensive. Then the occupants of the car you just bought a bumper for all claim whip lash, that money will then come from your own pocket.
The answer is to find a modification friendly insurer, it is not to drive an uninsured car.