Modify site frequented by ministers, it's said (5)
I believe the answer is:
alter
'modify' is the definition.
(I know that modify can be written as alter)
'site frequented by ministers it's said' is the wordplay.
'site frequented by ministers' becomes 'altar' (altar in a church).
'it's said' shows a homophone (sound like).
'altar' sounds like 'ALTER'.
(Other definitions for alter that I've seen before include "reform" , "Make changes to" , "Metamorphose" , "and 10 Across: Second self" , "Become different" .)