I tried searching for this and only found old posts. At the moment, what’s the best way of applying different organ registrations? In the older posts, it wasn’t yet possible using NotePerformer to assign different registrations to different manuals. Has this changed?
As I recall, NotePerformer uses MIDI controllers to handle organ registration changes, and there is a calculator here that will tell you the correct value for MIDI CC 103. It’s not really practical to define custom playing techniques to produce these controller changes given the complexity of the NotePerformer expression map, so your best bet would be to add Shift+X text and then add the necessary MIDI controller value in Play mode.
In Play mode, you can assign different instruments to different Dorico voices. So, the way to do this is run several instances of the NP organ patch for different Dorico voices, and then select the different manuals (great, swell, pedal) in the NP mixer.
You can then set the registration for each manual independently, as Daniel described.