If not white, rose replaced (9)
I believe the answer is:
otherwise
'if not' is the definition.
(synonyms)
'white rose replaced' is the wordplay.
'replaced' is an anagram indicator.
'white'+'rose'='whiterose'
'whiterose' is an anagram of 'OTHERWISE'.
(Other definitions for otherwise that I've seen before include "Alternatively" , "White rose (anag.)" , "in different circumstances" , "Differently - or else!" , "Under different conditions" .)