Change one's act? (4)

I believe the answer is:

turn

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This could be a double definition.

'change one's' is the first definition.
'turn' can be an answer for 'change' (turning is a kind of changing). I am not sure about the 'one's' bit.

'act' is the second definition.
(theatre)

Can you help me to learn more?

(Other definitions for turn that I've seen before include "rotation" , "Sour" , "Go off - act" , "Start" , "See 19" .)

I've seen this clue in the Evening Standard.

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