What exactly did you have to edit, and were you able to use the extra buttons on the sabertooth afterwards?
By default, for me, it installed to:
C:\Program Files (x86)\Frontier\EDLaunch\Products\FORC-FDEV-D-1003\ControlSchemes\DeviceMappings.xml
That holds the mappings.
To get your make & model number, use DXDIAG - it's on the input tab: Vendor & Product ID are the columns. It has to be plugged in.
The spare buttons (on my model) work fine because they only map to other buttons on the controller and all that is stored within the controller.
EDIT: (that's why I ordered up an x55 HOTAS rig. 2 limbs vs 4 (pedals not needed due to twist of controller) and there are just too many friggn buttons needed in the game so... *snicker* )