Notwithstanding the other debate in this thread about consent to sex versus consent to pregnancy, does your answer to the scenario above change even if you willingly plugged the needle into the arm yourself?

From my perspective, even if we assume the person plugged the needle into the arm, it's absolutely not my place to mandate that you must now keep the needle attached until the violinist can live independently again.

You may feel horrible about disconnecting that needle. We may even agree that it's a pretty awful thing to do to the violinist. In fact, we may even agree that you should be responsible for at least attempting to find alternative options for the violinist. But I certainly would never imagine creating a society in which we would prevent you from doing it. It is your body, and you should absolutely retain the right to revoke consent for the violinist to live off of it.