Mean to change moniker (4)
I believe the answer is:
name
'moniker' is the definition.
(I've seen this before)
'mean to change' is the wordplay.
'to change' indicates an anagram.
'mean' anagrammed gives 'NAME'.
(Other definitions for name that I've seen before include "By which one is known" , "celebrity" , "Amen (anag)" , "Designation; fame" , "''A rose by any other ... would smell as sweet'' (Romeo and Juliet)" .)