Changing fate is achievement (4)
I believe the answer is:
feat
'is achievement' is the definition.
(I've seen this in another clue)
'changing fate' is the wordplay.
'changing' is an anagram indicator.
'fate' with letters rearranged gives 'FEAT'.
(Other definitions for feat that I've seen before include "Achievement needing skill, strength, etc." , "Great deed" , "An accomplishment of fate" , "Notable act" , "Deed; achievement" .)