Retrospective user account merging

The email matching is only performed during the registration process. There's no way to do what you're saying because:
1) In Joomla, you can't update an email to one that's already in use by another user.
2) If we were to simply merge accounts when someone changed their email to match a social network account, there would have to be some extra validation, or else that would be a huge security risk.

With that said, the user can update a user's account with their social network, even if they've already linked it to another account. In the SCLogin module, there's an option for "Show Connect Account Button(s)". With that, when the Joomla user is logged in, they can click any of the social network buttons that they haven't already connected with and that social network account will be linked to their Joomla account. Even if that social network account was connected to a different Joomla user, the previous link will be broken and connected to the new account.

Beyond that, from an administrator's standpoint, if this happens a lot or you have a well-established Joomla site that you're adding social networking to, you can disable the Automatic Registration flow. With that, the user will go through a form-based flow, but you can actually show *no* fields there.. Just the "Login" portion, where they can login with an existing Joomla user or the Register side which just has a "Register" button. All the other fields can be disabled and imported or generated by JFBConnect.

I hope that helps explain and give you some ideas. If you have any questions, just let me know.

Thanks,
Alex