The undo function is assignable when assigned to a button via the act control surface. Generic surface does not expose it.

Is it possible to assign the faders/panners for busses instead of tracks? I just can't do it.

Where on my computer is the Control Surface files/data stored?
 
Update:
Found it - not that it does me any good.
HKEY_CURRENT_USER\Software\Cakewalk Music Software\ControlSurfaces\Presets\{404C9315-693D-4715-A326-143A992FA784}
 
Was hoping that there was a way to edit the data and avoid having to repeat the track parameter setup 40 times.
 

msr
I don't have X3, but I know this worked in X2. 
 
http://www.untidymusic.com/wordpress/using-sonar/setting-up-nanokontrol-sonar
 
You may need to "learn" the undo command.  Although I'm not sure if that is possible.
 
msr

Using X3c, Window 7 x64.
Following the instructions I was able to use the "Cakewalk Generic Surface" to control track level (fader), panning, mute & solo.  
 
Though not documented in the link you can also use the "Cakewalk Generic Surface" to map the Nano's play, stop, record, forward & rewind buttons - just select the appropriate radio button in Global Parameters (bottom right of the Control/Surface Property window) click & hold down the Learn button then hit the appropriate button on the NanoKontrol panel.
 
I was not able to get the ACT MIDI Controller to work at all or contribute any additional functionality.

I have the Play/Record/Stop, buttons programmed using the Global options.  I'm not much on MIDI so I don't know how I would manipulate the MIDI for that one global button.  I set the Nanokontroller up as an ACT device but I have no idea what to do and even with the built in definitions for what looks like a Nanokontroller it doesn't work at all.  Back to the Cakewalk Generic Surface as it is the only one that I can get working - everything except the one parameter I want.