A misfit can change with excessive zeal (10)
I believe the answer is:
fanaticism
'excessive zeal' is the definition.
(I've seen this before)
'a misfit can change' is the wordplay.
'change' is an anagram indicator.
'a'+'misfit'+'can'='amisfitcan'
'amisfitcan' is an anagram of 'FANATICISM'.
'with' is the link.
(Other definitions for fanaticism that I've seen before include "Zealotry" , "Excessive zeal" .)