Cannot demur, getting to change order (11)
I believe the answer is:
countermand
'order' is the definition.
'cannot demur getting to change' is the wordplay.
'getting' says to put letters next to each other.
'to change' indicates an anagram.
'cannot'+'demur'='cannotdemur'
'cannotdemur' with letters rearranged gives 'COUNTERMAND'.
(Other definitions for countermand that I've seen before include "Revoke; declare invalid" , "Recall" , "Revoke (an order)" .)