Captain replaces bandleader converting wine container to a library desk (6)
I believe the answer is:
carrel
'captain replaces bandleader converting wine' is the definition.
I can't tell whether this definition defines the answer.
'container to a library desk' is the wordplay.
'container' becomes 'car' (car is a kind of container).
'to a library desk' becomes 'rel' (I can't justify this - if you can you should give a lot more credence to this answer).
'car'+'rel'='CARREL'
Can you help me to learn more?
(Another definition for carrel that I've seen is " Small individual study area in a library".)