Modify some contractual terms (5)
I believe the answer is:
alter
'modify' is the definition.
(I know that modify can be written as alter)
'some contractual terms' is the wordplay.
'some' says the answer is hidden in the clue (some parts of the word are used).
'ALTER' is hidden in the letters of 'contractual terms'.
(Other definitions for alter that I've seen before include "Adapt" , "convert" , "Vary" , "Change, make different" , "Become different" .)