Oh, XenForo now has the ability to limit BBcodes to certain user groups? Interesting - AFAIK (and last time I checked the ACP for custom BBcodes) custom BBcode(s) are good for all users. What version are you using, as in my 1.5.8 I didn't see the ability to restrict them to certain groups.
Now, if you are talking about an add-on, that's a different matter.