Don't change this lad's headgear (7)
I believe the answer is:
stetson
'headgear' is the definition.
(Stetson is an example)
'don't change this lad's' is the wordplay.
'don't change this' becomes 'stet' (I've seen this before).
'lad' becomes 'son'.
'stet'+'son'='STETSON'
(Other definitions for stetson that I've seen before include "capital item" , "Style of hat" , "Felt hat" , "Hat, for Texan oil magnate, say" , "Man's hat with wide brim and high crown" .)