Can you elaborate what you mean by "anonymous for registered users"? That doesn't make any sense to me... Either a user is registered or not (e.g. anonymous). Khoros can allow posting anonymously, e.g. without logging in or registering, but I would definitely not recommend that as you will get flooded with spam.
If you mean that regular users that are registered and logged in should be able to post without their "user" attached to what they post: No, that is not easily possible at all and will need major customization, especially if there should really be no way of tracking the user "behind" the anonymous post... e.g. I would not recommend using Khoros for some kind of company internal whistleblower forum or something like that...
