Extra sub on, with change needed (5)
I believe the answer is:
bonus
'extra' is the definition.
(I've seen this in another clue)
'sub on with change needed' is the wordplay.
'with change needed' indicates anagramming the letters (letters changed around).
'sub'+'on'='subon'
'subon' with letters rearranged gives 'BONUS'.
(Other definitions for bonus that I've seen before include "Extra payment, may be performance-related" , "Extra payment for good work" , "Additional payment for work, often on merit" , "Extra payment - reward" , "Added extra" .)