Copied once, working with large note (6)
I believe the answer is:
cloned
'copied' is the definition.
(cloning is a kind of copying)
'once working with large note' is the wordplay.
'working with' is an anagram indicator (working with the letters).
'large' becomes 'l'.
'note' becomes 'd' (musical note).
'once' with its letters anagrammed with 'l' makes 'clone'.
'clone'+'d'='CLONED'
(Other definitions for cloned that I've seen before include "Produced a replica of" , "with many copies" , "eg Like Dolly the sheep" , "Copied genetically" , "Propagated like Dolly the sheep" .)