“If not a change for the worse" one put in (9)
I believe the answer is:
otherwise
'if not' is the definition.
(synonyms)
'a change for the worse one put in' is the wordplay.
'a change for' indicates an anagram.
'one' becomes 'i' (Roman numeral).
'put in' indicates putting letters inside.
'the'+'worse'='theworse'
'theworse' anagrammed gives 'otherwse'.
'otherwse' placed around 'i' is 'OTHERWISE'.
(Other definitions for otherwise that I've seen before include "White rose seen in a different way" , "As an alternative - like white rose" , "White rose (anag.)" , "in different circumstances" , "Under different conditions" .)