Mum wearing a shirt for a change (6)
I believe the answer is:
mutate
'a change' is the definition.
(I've seen this before)
'mum wearing a shirt' is the wordplay.
'mum' becomes 'mute' (to keep mum is to remain silent).
'wearing' is an insertion indicator.
'shirt' becomes 't' (as in a T-shirt).
'a'+'t'='at'
'mute' placed around 'at' is 'MUTATE'.
'for' acts as a link.
(Other definitions for mutate that I've seen before include "Change into something else" , "Me taut? (anag) - change fundamentally" , "Change in basic nature" , "(In genetics) change" , "Alter genetically" .)