Question: is it possible to uninstall the tuning kit (assuming you have the original exhaust still) and transfer it to a newer vehicle? I figure the physical exhaust should be no problem. How about the software tune specifically?

Parts yes, Tune no

Bear in mind that the JCW kit includes the head.

On a 3rd Gen car it is only a tune and exhaust system. No physical/mechanical changes to the motor.

Really? How much difference could only an exhaust/tune make?

quite a bit. the roadblock was the ECU, the tune opened the ecu up a bit.

Unfortunately, Mini (and all other car manufactures) really limit the true power of the car via the ECU

Welcome to turbocharged engines my friend. Out of the box, tuners have been able to make gains of 70hp+ on bone stock cars just by fiddling with the ECU's.

On a bone stock S (automatic transmission) with no additional hardware changes, easily +40WHP and +40Wqte on our Stage 1 Tune. Exhaust will probably give it an extra 15 t0 20 HP.