Favour clue virtually needing to be rewritten (10)
I believe the answer is:
indulgence
'favour' is the definition.
'clue virtually needing to be rewritten' is the wordplay.
'virtually' means to remove the last letter (all but the last letter).
'to be rewritten' indicates an anagram (I've seen 'being rewritten' mean this).
'clue' with its final letter taken off is 'clu'.
'clu'+'needing'='cluneeding'
'cluneeding' anagrammed gives 'INDULGENCE'.
(Other definitions for indulgence that I've seen before include "leniency" , "Gratification, luxury" .)