Make slight adjustments to great piece of music (4-4)
I believe the answer is:
fine-tune
'make slight adjustments to' is the definition.
(to make small improvements)
'great piece of music' is the wordplay.
'great' becomes 'fine' (fine can mean great in phrases like fine art).
'piece of music' becomes 'tune'.
'fine'+'tune'='FINE-TUNE'
(Other definitions for fine-tune that I've seen before include "Make small adjustments (to)" , "Improve, making small adjustments" .)