Change key with little hesitation (5)
I believe the answer is:
alter
'change' is the definition.
('alter' can be a synonym of 'change')
'key with little hesitation' is the wordplay.
'key' becomes 'alt' (I've seen this in other clues).
'with' is a charade indicator (letters next to each other).
'little hesitation' becomes 'er'.
'alt'+'er'='ALTER'
(Other definitions for alter that I've seen before include "Vary" , "Become different" , "reform" , "Alert to change" , "Change, make different" .)