Change some legal term (5)
I believe the answer is:
alter
'change' is the definition.
(I know that change can be written as alter)
'some legal term' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'ALTER' can be found hidden inside 'legal term'.
(Other definitions for alter that I've seen before include "Vary" , "and 10 Across: Second self" , "Bout of extravagant spending" , "Change or adjust" , "convert" .)