And that code is pretty much what I was doing but will keep my mouth shut before I try it.

Good thing I saved all my stuff before reboot because every darn sketch I'd worked at for the last week or so had it's Whatever.ino deleted from its directory afterwards.
Will look at again after dark. I have a T2 with 3 buttons and two pots and Din Midi and use it as a workshop Controller/Merger/usb-Midi interface.

With Carlos's query in mind, I'd ducked into it's code as a refresher as I'd left a choice of lines to comment in or out for different modes and had worked out two different ways of doing Merge.