Can the FC7 pedal be used to control after touch?
A straightforward change (like setting FC to control the Super Knob) is not possible according to the manual. A possible workaround, I guess would be this: since "Aftertouch" is just a control source you could just edit part modulation matrix changing source to "FootCtrl1" or "FootCtrl2" wherever "Aftertouch" is selected. This would have to be done for every part in a performance.
Can the FC7 pedal be used to control after touch?
No, the FC7 can be assigned to any Control Change 1-95 (except 32), or the Super Knob, on a per Performance basis. Aftertouch, in MIDI, is its own category of message. It is generated when additional pressure is applied to an already struck key. And like the Pitch Bender message (generated by a dedicated Wheel), Aftertouch, is generated by a single dedicated method (the sensor in the keybed).
What is your application?
What are you envisioning doing with your FC7?