Modify church table, reportedly (5)
I believe the answer is:
alter
'modify' is the definition.
(I know that modify can be written as alter)
'church table reportedly' is the wordplay.
'church table' becomes 'altar' (ceremonial table in a church).
'reportedly' indicates a 'sounds like' (homophone) clue.
'altar' sounds like 'ALTER'.
(Other definitions for alter that I've seen before include "Make changes to" , "Vary" , "Change, make different" , "Revise" , "and 10 Across: Second self" .)