Reportedly modify what's needed for mass (5)
I believe the answer is:
altar
'what's needed for mass' is the definition.
(table used in a church service eg Mass)
'reportedly modify' is the wordplay.
'reportedly' shows a homophone (sound like).
'modify' becomes 'alter' (I've seen this before).
'alter' sounds like 'ALTAR'.
(Other definitions for altar that I've seen before include "Place of sacrifice" , "Table used for the mass or eucharist" , "Focal point for Mass" , "location for union negotiation" , "Communion table" .)