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