Acknowledges it's mad to change (6)
I believe the answer is:
admits
'acknowledges' is the definition.
('admit' can be a synonym of 'acknowledge')
'it's mad to change' is the wordplay.
'to change' is an anagram indicator.
'its'+'mad'='itsmad'
'itsmad' with letters rearranged gives 'ADMITS'.
(Other definitions for admits that I've seen before include "Allows in or accepts guilt" , "Lets in and confesses" , "Confesses or allows to enter" , "Owns up or lets in" , "Owns up or grants entrance to" .)