I know the question about quickly changing the content of external output has been raised before. The typical case would be a navigator with a tablet on the rail wishing to change the value of a mast jumbo display to show time to layline/ time to mark or similar. https://expedition.boardhost.com/viewtopic.php?id=1426
 
How about a “map channel to external output” function from the “Edit number box” menu (right clicking the number box)?
 
To change the content of a mast jumbo, one could simply set the display to always show “External 1”, then as the race goes on one could right click the number box showing the value of interest and select “map channel to external 1” – done.
 
As long as the value is set up in a number box, it should be a quick 2 click operation instead of going through the instruments settings and resetting the channel from there.