Batter? It's suet but it's a replacement! (10)
I believe the answer is:
substitute
'a replacement' is the definition.
('substitute' can be a synonym of 'replacement')
'batter? it's suet but' is the wordplay.
'batter?' indicates an anagram (I've seen 'battered' mean this).
'its'+'suet'+'but'='itssuetbut'
'itssuetbut' anagrammed gives 'SUBSTITUTE'.
'it's' acts as a link.
(Other definitions for substitute that I've seen before include "Reserve" , "deputy" , "Acting" , "Stand-in" , "Stand in" .)