Take over from peers used to reform (9)
I believe the answer is:
supersede
'take over from' is the definition.
(I've seen this before)
'peers used to reform' is the wordplay.
'to reform' is an anagram indicator.
'peers'+'used'='peersused'
'peersused' is an anagram of 'SUPERSEDE'.
(Other definitions for supersede that I've seen before include "Take the place of, override" , "Stop using" , "Supplant, replace" , "Take the place of, supplant" , "set aside" .)