Alter appearance to conceal identity (8)
I believe the answer is:
disguise
'alter appearance to conceal identity' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for disguise that I've seen before include "Camouflage, mask" , "Change of appearance for concealment" , "Clothes etc misleading as to identity" , "Camouflage to hide identity" , "Cover" .)