idkwhatusername except for Twitter, the process is currently fully based on email match, so this is actually not possible without changing the current implementation.
I believe we have some sort of support in Flarum core for social linking but the API might be incomplete and this extension currently doesn't use it.
Twitter is an exception and uses a custom column on the users table, so a connect/disconnect for Twitter could probably be done with slightly less work than the other providers.
