apart from the keys, what is there to re-code if its the same type (engine) ECU?
the immobiliser box

the keys are coded to the immobiliser box, and the immobiliser box is coded to the ecu. if you swap ecu, you can match it to the old immob box easily with vag com, though it needs to be a 'registered' copy. if you change the box or keys things get tricky, you need vag-tacho to get the skc code, and you can only get that if you have matched key in the ignition.
if you get a matched immob box and chip you can fit these to your car and old key, then do the ecu recode thing, but we are digressing from the thread a bit now
