One other note to let you know that I am thinking about the same thing you are....

On my jet I am mixing smoke with brakes on a Futaba 9C. I am using multiple P-mixes and offset mixes to do this so that I can only turn on smoke when gear are up and if I land with smoke ON I have no brakes. Offsets are added and P-mixes are never cancelled.

So setting up multiple mixes just adds them together. There is not an override to move a servo to a certain position that I have seen with a Futaba radio.

(Don't get me wrong though -- I have only recomended Futaba for the last 30 yrs!!!)