Mine changed in appearance (4)
I believe the answer is:
mien
'appearance' is the definition.
(I've seen this in another clue)
'mine changed' is the wordplay.
'changed' indicates anagramming the letters.
'mine' anagrammed gives 'MIEN'.
'in' acts as a link.
(Other definitions for mien that I've seen before include "Counterance - mine?" , "Dignified manner" , "A manner like mine" , "aspect" , "A countenance like mine" .)