Hold the top part of the card (above the plastic blister) with the car face down. Use a Q-tip to dab acetone on the back of the card along three sides of the seal . . . don't wipe it in or the ink on the back might smear. Most Matchbox or Hot Wheels have colored writing along one edge under the seal . . . leave that one alone. Once the acetone soaks through the cardboard it will desolve the glue and the weight of the car will separate the blister from the card hinged from the one attached side. Pull the car out, do whatever you want to it, put it back in and glue it down with a very tiny bead of super glue.
A guy I work with has won a national model car contest in Atlanta for the past 3 years and has just started customizing die cast cars. He showed me three and there was only one that I could tell had ever been tampered with . . . and that was only because I knew what he had done to it and I spent a few minutes inspecting it.
