Quick to agree a change (5)
I believe the answer is:
eager
'quick' is the definition.
(thesaurus)
'agree a change' is the wordplay.
'a change' is an anagram indicator.
'agree' with letters rearranged gives 'EAGER'.
'to' acts as a link.
(Other definitions for eager that I've seen before include "Swiss mountain" , "Whole-hearted" , "Low platform" , "Keenly interested" , "Keen, avid" .)