Can I define users by groups, to use some MACs for an SSID and the some other MACs for other different SSID. How can I do this?. Creating a new role?
Yeah you can do this but if you have a small number of users, and if you have a large number of users as Tim said, You have to go for CPPM.
For doing that first you have to create one user role and then add the users MAC ids on that, after that in AAA profile just select the user derived role from the drop down list. So it will overwrite your default role and make them work.