Change routine (4)
I believe the answer is:
turn
This clue is a double definition.
'change' is the first definition.
(turn is a kind of change)
'routine' is the second definition.
('turn' can be a synonym of 'routine')
(Other definitions for turn that I've seen before include "(Of tide) change from flood to ebb" , "revolutionary act" , "Go off - act" , "Go off - performance" , "Swing round" .)