Fourth mate replaced by first officer — alleged to be different (8)
I believe the answer is:
assorted
'different' is the definition.
(similar in meaning)
I cannot understand how the remainder of the clue works.
(Other definitions for assorted that I've seen before include "Classified" , "like some chocolates" , "Manifold" , "Of various types put together" , "Stared so at a varied mixture as of sweets" .)