Vicar joining a reactionary PM for restoration project (6)
I believe the answer is:
revamp
'restoration project' is the definition.
(a revamp is a makeover or restoration)
'vicar joining a reactionary pm' is the wordplay.
'vicar' becomes 'rev' (reverend).
'joining' means one lot of letters go next to another.
'reactionary' says the letters should be written in reverse (reactions happen in the opposite direction).
'pm' back-to-front is 'mp'.
'rev'+'a'+'mp'='REVAMP'
'for' acts as a link.
(Other definitions for revamp that I've seen before include "Patch up or renovate" , "Make new, improve or up-date" , "Give new appearance to" , "face-lift" , "Refurbish" .)