well, it's been a _long_ time missing function. if one can assign one
channel preset, why can't the same be reset unassigned, just for closure,
functional completeness sake?
iirc, there were some requests on this regard from time to time, that is,
a way to set one channel silent, unassigned, with no preset, permanently.
If the goal is channel muting, IMO the solution should be a channel mute
function, with a precise name and strict semantics, without collateral
effects. It is not necessary to link the mute status of a channel to it's
assigned program, and separating both states would be more useful.