Indeed it makes good sense what Raymond List suggested! I think it is the best logic for this particular instrument!
Therefore, I prepared a new ODF 1.1 with the behavior:
Chamade Trumpets are not affected by couplers
Chamade Trumpets are not affected by Unison off
This is achieved by placing the Chamade Trumpets on a hidden dedicated division. Drawing the corresponding Chamade stop button will couple the Trumpet to any desired keyboard or pedalboard.
Hence, you can couple divisions together to a specific keyboard and silence another keyboard using Unison off. Then, on the silenced keyboard you can play the Chamade Trumpet against the chorus.
I need volunteers to test this ODF, to find out any possible drawbacks of this logic. One comes immediately to my mind: the Chamade Trumpet will not be compatible with Hauptwerk Master Couplers, since now it stays on a windchest (forming a keyboardless division) of its own. Hauptwerk Master Couplers work on keyboards, not on divisions, and therefore a division without a dedicated keyboard is not accessible for the Master Couplers. I believe it is not a problem for this particular instrument, since the Chamade Trumpet is available on all the keyboards via dedicated drawstops.
If you wish to test the new ODF, please write an e-mail to me. When the ODF is sufficiently tested, I will release it publicly on my web pages.