Hag to change, but not initially (5)
I believe the answer is:
witch
'hag' is the definition.
(synonyms)
'change but not initially' is the wordplay.
'change' becomes 'switch' (switching is a kind of changing).
'but not initially' means to remove the first letter.
'switch' with its first letter taken off is 'WITCH'.
'to' acts as a link.
(Other definitions for witch that I've seen before include "Black cat and broomstick owner?" , "One supposed to have magical powers" , "Broomstick riderof children's tales" , "Enchantress" , "charming female" .)