Spice Girl goes over old hit, occasionally sounding tuneful (7)
I believe the answer is:
melodic
'sounding tuneful' is the definition.
(having a melody or tune)
'spice girl goes over old hit occasionally' is the wordplay.
'spice girl' becomes 'Mel C' (member of the Spice Girls).
'goes over' means one lot of letters goes inside another (to go over can mean to wrap around).
'occasionally' indicates alternate letters.
'old'+'hit'='oldhit'
The alternate letters of 'oldhit' are 'odi'.
'melc' enclosing 'odi' is 'MELODIC'.
(Other definitions for melodic that I've seen before include "Of music, tuneful and sweet" , "Pleasantly musical" , "Pleasant-sound" , "Harmonious" , "nice on the ear" .)