I would be interested in this as well. I see we can create different categories for smilies. I would like to be able to define what usergroups could use smilies from that category, but I would like everyone to see them. This creates a benefit of people being able to use and show off smilies if they are in a certain usergroup.
Let's say I add a smilies defined by the text "bigsmile" that only paid members could use. Everyone could see the smilie, but when someone not in the usergroup tried to use it, it just displayed the bigsmile text.