Last word written by Dickens' first editor corrected (7)
I believe the answer is:
amended
'corrected' is the definition.
(amending is a kind of correcting)
'last word written by dickens' first editor' is the wordplay.
'last word' becomes 'amen' (I've seen this before).
'written by' is a charade indicator (letters next to each other).
'first' says to take the initial letters.
'editor' becomes 'ed'.
The first letter of 'dickens' is 'd'.
'amen'+'d'+'ed'='AMENDED'
(Other definitions for amended that I've seen before include "Corrected" , "Carried out reforms" , "Made changes to correct" , "Revised or altered" , "Modified for the better" .)