Sauciest hint changed, becoming zealous (12)
I believe the answer is:
enthusiastic
'zealous' is the definition.
('enthusiastic' can be similar in meaning to 'zealous')
'sauciest hint changed' is the wordplay.
'changed' indicates an anagram.
'sauciest'+'hint'='sauciesthint'
'sauciesthint' is an anagram of 'ENTHUSIASTIC'.
'becoming' acts as a link.
(Other definitions for enthusiastic that I've seen before include "Intensely keen and interested" , "Showing keen interest" , "Full of fervour" , "Gung-ho" , "Ardent, zealous" .)