Subtle changes in old garment (6)
I believe the answer is:
bustle
'old garment' is the definition.
(historical item of clothing)
'subtle changes' is the wordplay.
'changes' indicates an anagram.
'subtle' is an anagram of 'BUSTLE'.
'in' acts as a link.
(Other definitions for bustle that I've seen before include "Excited activity - or padding at rear of old skirt" , "Attachment to a Victorian woman" , "Frame under a dress" , "Hurried activity - old padded support for woman's dress" , "Busy activity; old skirt padding" .)