Hiya Mark, welcome to Saabscene
I think you will find that only the upgrades by Hirsch will not affect your warranty, they are also the dearest
Other tuners such as Speedparts / BSR see
www.elkparts.co.uk and Maptun see
www.maptun.co.uk are available and do make a huge difference to your car but will affect the warranty.
Speedparts do a PPC system where you plug a hand held device into your car and perform the upgrade, you can also return it to standard form when ever you wish, again see
www.elkparts.co.uk
All the companies I have listed above do upgrades that are specific your auto transmission and keep the car drivable, in fact most of us have found our upgraded cars to run smoother as well as being more capable, not to mention more fun
Hope that helps Chris