Musical dramas back to back, merging in effect (9)
I believe the answer is:
operative
'in effect' is the definition.
(similar in meaning)
'musical dramas back to back' is the wordplay.
'musical' becomes 'opera' (I've seen this before).
'dramas back' becomes 'evit' (I can't explain this - if you can you should give a lot more credence to this answer).
'to back' shows that the letters should be reversed in order.
'evit' in reverse letter order is 'tive'.
'opera'+'tive'='OPERATIVE'
'merging' acts as a link.
This may not be correct. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for operative that I've seen before include "Functioning; worker" , "Significant" , "Efficient" , "American detective" , "undercover agent" .)