Something unusual I try to change under artist (6)
I believe the answer is:
rarity
'something unusual' is the definition.
(I've seen this before)
'i try to change under artist' is the wordplay.
'to change' indicates anagramming the letters.
'under' says to put letters next to each other.
'artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
'i'+'try'='itry'
'itry' with letters rearranged gives 'rity'.
'rity' put after 'ra' is 'RARITY'.
(Other definitions for rarity that I've seen before include "Something not often seen" , "Unusual specimen" , "Uncommon item or event" , "Something very scarce, probably valuable" , "Infrequent occurrence" .)