Hi Mike ! I'm back in Athens.
I use extensively the programm change commands all my playin' life, so Hauptwerk and of course GrandOrgue won't be excluded from my treatment.
The electronic organ that I use to control them (as you may know by now) is the Yamaha EL900 (1998 model). This one was the definitive series model and the last of a long generation of organs. Has 16 registration buttons located between the two manuals whitch send also MIDI program change command on ch16 only for the entire organ and for programs 1~16(as are the registrations) - Up Manual on ch1 or ch4, lower man on ch2 or ch5, pedalboard on ch3, expression ped on ch16-control no11, footped on ch16-control no4, no sustain send(no64), but the two switches on expr ped send only system exclusive code..
I tell you all this to know the system cause I'm gonna ask you something later.
So, with the reg buttons & 2 footpedals I can have full control of small to medium VPOs and some great VPOs with the help of reg set on softwere.
Example : small chappel organ with 8 stops and some couplers ~ assign reg buttons 1 to 8 one each for the 8 stops and 4 more for swell to Grt, Grt to ped, swell to ped, swell tremulant ~ assign exp ped (no11) to swell ped and the control of the VPorgan is complete. Oranists wanna do this for on the spot control of their instrument and instant access of every stop for mixing~unmixing.
For medium VPOs I follow the same attitude but with full 16 reg complete.
On biger organs I got problem of assign lets say 28 stops plus couplers and tremulants to just 16 buttons, so I make use of the registration sets of the VPO (only16 of them ~ only 16 combinations of stops/couplers memorized) and reassign the exp ped11 to cressendos ped and the footped4 to swellped. So far so good, I'm O.K. with it.
With all this work I can change colours of my sound depending on the organ piece I'm workin'on, is not much but this that I can afford for now and I make the best of what I have in hand.
So, to your MIDI commands.
Hauptwerk responds in all MIDI thing I'm sending, sometimes gives me alternatives to solve a problematic situation and at the end it works as I want it to work.
GrandOrgue on the other hand(both versions v.1&v.2, my organ also) do not.
a. Program change.
v.1 opens his reg set no1 at my command reg(prog ch no) no12 and so on 'till set no 5 (pr change 16) and only on the old St.-Mockers organ(witch has 60 reg sets!). The other organs and harpsichords do not respond to any progr ch command from EL900.
v.2 do not respond at all...
Both respond on their program numbers(1~100) on the right of their screen, also to the system exclusive sends from my switch pedals(!) - they change their programs but no stop/coupler/reg sets
b. Continuous controls.
Both respond to swell ped commands but I had to search for witch endorsment of the 5 is the appropriate ... usualy No3
My question : why this happens to GrandOrgue, and why in Hauptwerk don't?
I didn't try to do all this with my synths&piano mother 'cause I want o play VPOs with my EL900 organ, so it doesn't matter if they can command or Grand Orgue can not respond to them.
To your question, changing reg set changes all of the organ settings. There are exeptions however, but the SET depends on the organists favor/needs/fantasia, also the row can be set according to one's program of performance, anyway it's a helping hand for quik change of sound, expression ect.
Enough for now
see what you can find
cheers
Panos