Change Greek character at famous gallery (6)
I believe the answer is:
mutate
'change' is the definition.
(mutating is a kind of changing)
'greek character at famous gallery' is the wordplay.
'greek character' becomes 'mu' (letter from the Greek alphabet).
'at' says to put letters next to each other.
'famous gallery' becomes 'tate' (Tate Modern, Tate Britain etc. I am not sure about the 'famous' bit.).
'mu'+'tate'='MUTATE'
Can you help me to learn more?
(Other definitions for mutate that I've seen before include "Change genetically" , "Gradually change form" , "Alter genetically" , "Change genetic structure" , "Change in genetic way, perhaps from radiation" .)