Copper gets gear changed, some of it good, some of it bad (7,3)
I believe the answer is:
curates egg
'some of it good some of it bad' is the definition.
(curate's egg refers to something of mixed quality)
'copper gets gear changed' is the wordplay.
'copper' becomes 'cu' (chemical symbol).
'changed' indicates an anagram.
'gets'+'gear'='getsgear'
'getsgear' is an anagram of 'ratesegg'.
'cu'+'ratesegg'='CURATES EGG'
(Other definitions for curates egg that I've seen before include "Something good in parts" , "Get ace rugs (anag)" , "I'm good, but only in parts" , "Something partly good / bad" , "A thing good in parts" .)