Composer in debt took on too much (7)
I believe the answer is:
overdid
'took on too much' is the definition.
(eg overdid it at work)
'composer in debt' is the wordplay.
'composer' becomes 'verdi' (Italian composer Giuseppe Verdi).
'in' is an insertion indicator.
'debt' becomes 'OD' (abbreviation for overdraft).
'verdi' put into 'od' is 'OVERDID'.
(Other definitions for overdid that I've seen before include "went too far" , "Made too much of" , "Exaggerated" , "operated excessively" .)