Change theatrical act (4)
I believe the answer is:
turn
I believe this clue is a double definition.
'change' is the first definition.
(I know that turn is a type of change of course)
'theatrical act' is the second definition.
(turn can mean a performance in a show)
(Other definitions for turn that I've seen before include "Move in a new direction" , "Go; spin (cricket)" , "roll" , "Revolve; act" , "Refuse" .)