Note sure I would take the route of changing the VIN on an NSR to a VIN from some other bike. The last thing I would worry about at that point is the bike getting impounded, I would be more worried about the potential felony charges you could be facing from that.

Have you tried to go about it the legal way? You know... getting it titled/registered as a Honda NSR250? Go spend some time on the DMV's website and read through all the information they have on registering a non-titled vehicle.