In a good position, but not to revise a musical work! (2,3)
I believe the answer is:
on top
'in a good position' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'not to revise a musical work' is the wordplay.
'to revise' is an anagram indicator.
'a musical work' becomes 'op' (abbreviation for opus).
'not' anagrammed gives 'ont'.
'ont'+'op'='ON TOP'
'but' is the link.
Can you help me to learn more?
(Other definitions for on top that I've seen before include "At the summit or in superior position" , "Winning" , "In a dominant position" , "Leading" .)