Yes, you can. If you go to your server settings, go to 'License' and then hit the 'Assignments' tab, you'll find what you're looking for.
Here, you can both reserve and set a max for the number of agents connected to a System Profile and specific Agent Groups of the Profile.
Be sure to check the box for 'Enable License Assignments' though. I've made the mistake of creating assignments but never checking that box before 🙂
Hope this helps,