Rue arrest when changing financial officer (9)
I believe the answer is:
treasurer
'financial officer' is the definition.
(synonyms)
'rue arrest when changing' is the wordplay.
'when changing' indicates anagramming the letters.
'rue'+'arrest'='ruearrest'
'ruearrest' is an anagram of 'TREASURER'.
(Other definitions for treasurer that I've seen before include "Financial officer" , "who's got hold of the cash?" , "Book-keeper" , "One who highly prizes" , "Official in charge of funds" .)