How do you program a patch change on a Nord stage 3 to also change to a specific rackspace in GP?
If you want to do it from the Nord, you would have to find out from them how to arrange to send out the desired program changes from it.
And you can check, using the GP MIDI Monitor if a Program Change is properly sent. Then you can modify a Variation to react to this specific PC.
Take a look at the user manual page 42