Second in command, type due largely to be replaced (6)
I believe the answer is:
deputy
'second in command' is the definition.
(I've seen this before)
'type due largely to be replaced' is the wordplay.
'largely' means to remove the last letter.
'to be replaced' is an anagram indicator.
'type'+'due'='typedue'
'typedue' with its final letter removed is 'typedu'.
'typedu' with letters rearranged gives 'DEPUTY'.
(Other definitions for deputy that I've seen before include "Not the principal" , "Person acting on behalf of another" , "One who stands in" , "Second in command" , "Second-in-command" .)