Mine changed in manner (4)
I believe the answer is:
'manner' is the definition.
(mien can mean a manner or attitude)
'mine changed' is the wordplay.
'changed' is an anagram indicator.
'mine' is an anagram of 'MIEN'.
'in' is the link.
(Other definitions for mien that I've seen before include "A face - maybe mine" , "Comportment" , "Dignified manner" , "The carriage" , "A person's demeanour" .)