Not a change for the better (7)
I believe the answer is:
relapse
'better' is the definition.
The definition and answer can be both related to change as well as being verbs in their base form.
Perhaps you can see an association between them that I don't see?
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for relapse that I've seen before include "Get worse again" , "Fall back into old ways" , "Repeals (anag.)" , "medical problem" , "Become ill again" .)