There are some control units which can be re-used/coded. You have to check in the initial report (E-series cars) or vehicle status report (F/G-series cars) and check for errors stating that a control unit is incompatible. Later F/G series cars are the biggest issue as most of the control units are chassis protected. EGS (mechatronics) on cars with the later GWS (fly by wire) gear lever cannot be fitted as a used part to another car, you will not be able to select Drive. Additionally, any control unit connected to the immobiliser system cannot be fitted as a used part.