I have an internal section in my Joomla only for "Registered" users. There they can edit preferences. Multiple users can access the same preferences (different stakeholders). Now I have "smithcorp" and "smithcorp_guest". They should both be able to view the same things, but "smithcorp_guest" shouldn't be able to edit the preferences. Is there a way to forbid "smithcorp_guest" access to this page? I have only seen access regulation via the user level, i.e. unregistered, registered, admin.
There's also "special access" which is essentially anyone that has a higher access level than simply "registered". If you require more granularity there are extensions which will allow this, but they do get somewhat complicated. Just check out http://extensions.joomla.org/extensions/access-a-security, but I highly recommend reading the documentation and doing testing before deploying any of those solutions to a live site, as they can be quite difficult / non-intuitive.