User blog comment:G0LD3NF1RE/Werewolves Appearing in Skyrim/@comment-2162365-20111108162519/@comment-152.133.14.7-20111108172800

I would think so, in Oblivion you could be cured of Vampirism and then contract the disease again (but the quest to get cured was so obnoxious that most ppl don't bother to switch back and forth). It sounds like the Circle in Skyrim is a bit more ritualistic and involves some kind of commitment to their little guild-within-the-guild, so it may be a one time thing for werewolves.