Reportedly, modify part of church (5)
I believe the answer is:
altar
'part of church' is the definition.
(I've seen this before)
'reportedly modify' is the wordplay.
'reportedly' indicates a 'sounds like' (homophone) clue.
'modify' becomes 'alter' (I've seen this before).
'alter' sounds like 'ALTAR'.
(Other definitions for altar that I've seen before include "Sacrificial slab" , "Table used for religious ceremony" , "Sacrificial table" , "High table for religious ceremonies" , "place of unions" .)