I do believe Revo and APR are the only top tuning companies to have attempted a remap on the RS3 but I could be wrong. The ECU has to be removed for the process. An ASN member from Glasgow got his done recently and the ECU was sent away to get remapped and he is a happy man apparently. Many tuning companies online state that their remaps are "undetectable" and this simply isn't true. While it may not be physically apparent it is relatively easy to find out by comparing the contents of the ECU with a standard one, by verifying the checksum (a value calculated against the contents of the ECU), and by taking the vehicle for a test drive and taking some logs of the data provided by the ECU. Remapping is NOT undetectable, and don't let anyone tell you different. Many dealerships are aware of remaps and are not scared of them, some even offer them! - Audi use MTM. It is important to note that a manufacturer cannot refuse a warranty claim on your car because it is remapped, they would have to prove that any failure was directly caused or affected by the remap. Hope this of use.