About to get costume right (7)
I believe the answer is:
redress
'right' is the definition.
('redress' can be a synonym of 'right')
'about to get costume' is the wordplay.
'about' becomes 're' (regarding**).
'to get' says to put letters next to each other.
'costume' becomes 'dress' (I've seen this before).
're'+'dress'='REDRESS'
(Other definitions for redress that I've seen before include "Set right - compensation" , "Pay" , "Prepare again - satisfaction" , "relief" , "Get back into gear" .)