Three manuals into one or two - MIDI channel switch Query

Is this possible without using the couplers? Using just one keyboard (the Great) is it possible, with a single button, to make it play as either the Swell or the Choir without sounding what is already set on the Great. When I get my two-manual organ, can I make the top keyboard play as either the Swell or the Choir without cancelling registrations of either. I appreciate this is probably a MIDI channel change, so it might be impossible. What do you do when you don't have enough keyboards? I do love Organteq!