Change of rate more certain for financial official (9)
I believe the answer is:
treasurer
'financial official' is the definition.
(a treasurer manages finances)
'change of rate more certain' is the wordplay.
'change of' is an anagram indicator (the letter order is changed).
'more certain' becomes 'surer' ('sure' can be similar in meaning to 'certain').
'rate' anagrammed gives 'trea'.
'trea'+'surer'='TREASURER'
'for' is the link.
(Other definitions for treasurer that I've seen before include "he's got the money" , "Club official" , "Money dealer" , "Association member guarding the cash" , "Committee member" .)