If you have the crutchfield wiring harness, and you can get the old head unit out, it shouldn't be very hard at all. Assuming you have something like a Becker Grand Prix, the only irreversable step would be having to remove the little locking tabs that hold the heat unit in place, but even then I think you could reinstall it, and it would just be a friction fit kind of thing. With the harness adapter, it should just plug straight together.