Pagans adding verse to biblical book (7)
I believe the answer is:
vikings
'pagans adding' is the definition.
I can't judge whether this definition defines the answer.
'verse to biblical book' is the wordplay.
'verse' becomes 'v'.
'to biblical book' becomes 'ikings' (I can't explain this - if you can you should give a lot more credence to this answer).
'v'+'ikings'='VIKINGS'
(Other definitions for vikings that I've seen before include "Scandinavian marauders" , "Scandinavian adventurers who attacked Ireland" , "Invaders" , "Norsemen" .)