I'm specifically inquiring about the 1996 GTS PCM.

The question is are then unused PCM pins that can be used for nitrous control? Some people program the AC pin for nitrous in other cars (if there is no AC.) Need at least 1 for a dash nitrous on/off switch to tell the PCM. And possibly another pin from the PCM to control the actual nitrous solenoids.

If no pins are available, how do they pull some timing out for nitrous? Or do they just pull back the timing a couple degrees whether nitrous is being used or not?

If the PCM can support a dash toggle, that could also be used for 2 fuel octane timings.