Before Spring loses the head - fickle type is one of those who can go either way (15)
I believe the answer is:
interchangeable
'before spring' is the definition.
Both the answer and definition are adjectives. Perhaps there's a link between them I don't understand?
'loses the head fickle type is one of those who can go either way' is the wordplay.
I cannot quite see how this works, but
'one' could be 'an' (I've seen this in other clues) and 'an' is found in the answer.
'can' could be 'able' (I've seen this in other clues) and 'able' is located in the answer.
'way' could be 'n' (Compass direction - North) and 'n' is found in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for interchangeable that I've seen before include "(Of things) that may be swapped over" , "that can be traded in places" .)