Part of church/state reform! (5)
I believe the answer is:
alter
'reform' is the definition.
(thesaurus)
'part of churchstate' is the wordplay.
I cannot quite understand how this works, but
'part' could be 'te' (te is a kind of part) and 'te' is present in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for alter that I've seen before include "Revise" , "Change, maybe later" , "reform" , "Change, modify" , "Vary" .)