They made it illegal to swap IDs between cars because it's too easy to write off your own car and then steal an identical one and replace its ID with yours. Then it is easy to sell yours as a good one and no-one can trace that it's actually a stolen car. This isn't much of an issue with our cars these days as it isn't easy to steal one to order. On current model cars it is pretty easy to find one the same to ring. The downside of this law is that it's also impossible to reshell a car with a second hand shell and keep the original ID. You might be able to keep the original ID under the points scheme but you still need receipted proof of where the shell came from.