Isn’t it easy to send a newsletter to all saying “you are subscribed you can manage your subscription here” and add the profile_url tag or directly the unsubscription_url tag?
Here’s what I did: I exported the subscribers to a file, edited all of them to have the status that I wanted (“C”=Confirmed, “S”=Subscribed, which means unconfirmed), and then I re-imported them back to Newsletter.