Michael D wrote:HOWEVER, NOW I am not clear on how to get Reaper to record stop changes...
There's another way to let your Sequencer handle your Registration changes. For a given piece of music (MIDI file), on a given Hauptwerk Sample Set... create a Stack of Registrations in the Registration Stepper, so that by pressing "Stepper Plus" at the appropriate moments, you run through all of the Registrations, in order, required for the performance of that piece.
Then set the Organ such that the "Stepper Plus" is triggered by a simple MIDI message that cannot be generated unless you intend it. For example, trigger by "Note ON", middle C, on Channel 8.
Then in your MIDI file, create a "Registration Track"... on Channel 8, with nothing else using Channel 8... and then enter a "Middle C" at the appropriate moments in your Score for each change of Registration.
If you need to record Registration Changes made spontaneously during Live Play, you can do this using the built-in Hauptwerk MIDI Recorder. Then playing back this recording within Hauptwerk (on the same Sample Set) will correctly reproduce all of your Registrations, such that they can be captured (saved to a Piston during playback?) and documented. These results could then be used to set up the Registration Stepper to use as outlined above.
Good Luck!