This article talks about both unreadable and fake plates. I think you're talking about unreadable plates.

In that case you remove your tape or other obstruction before the inspection and put it back right after.

The police in New York support this kind of obstruction when done by the right people. The person quoted in the article removed an obstruction from a license plate of a car parked on the street. The driver called the cops, who took the side of the person evading traffic law.