The tool you are thinking of is the RS Tuner. It allows base maps to be uploaded to your car and then swapped with the oem one at any time.
RS tuning, Ktec, Superchips and Henk all do their own versions. Once you plug the box in it will code to your car so you can't borrow someone else's and use it in your car.
Best off getting a proper custom map on a rolling road to be honest.