Leave the stage once tune changes? (6)
I believe the answer is:
exeunt
'leave the stage' is the definition.
(I've seen this before)
'once tune changes?' is the wordplay.
'once' becomes 'ex' (prefix meaning former or onetime).
'changes?' is an anagram indicator (I've seen 'change' mean this).
'tune' is an anagram of 'eunt'.
'ex'+'eunt'='EXEUNT'
(Other definitions for exeunt that I've seen before include "(Actors) depart" , "They leave (stage direction)" , "Stage direction (Latin, they go out)" , "direction to get cast away" , "(Actors) leave stage" .)