Style I had or changed (6)
I believe the answer is:
hairdo
'style' is the definition.
(I've seen this before)
'i had or changed' is the wordplay.
'changed' indicates anagramming the letters.
'i'+'had'+'or'='ihador'
'ihador' with letters rearranged gives 'HAIRDO'.
(Other definitions for hairdo that I've seen before include "Coiffure (colloq.)" , "The process of styling hirsute head" , "Bob, perm or bouffant" , "Styling of the locks" , "capital arrangement" .)