Right, I just wanted to make sure you knew that when the DIN midi is disabled when USB is connected. What you described should work.
I can confirm that this works. I can edit the connected stompboxes in H9Control, and simultaneously control and sync them over midi. What I call the “auxilliary midi input” fortunately is a global H9Control setting, so the incoming clock and midi CC’s are distributed to all the devices, regardless of which one is active. That’s a pretty neat implementation.
Thanks for your concern.