Change, modify (5)
I believe the answer is:
alter
I believe this clue is a double definition.
'change' is the first definition.
(I know that change can be written as alter)
'modify' is the second definition.
(I know that modify can be written as alter)
(Other definitions for alter that I've seen before include "Change, maybe later" , "Change or adjust" , "Vary" , "Bout of extravagant spending" , "and 10 Across: Second self" .)