Thanks for re-posting,
First off, it helps if you are running the latest firmware from Mimosa. (2.4.1)
Secondly, the way you want to do this depends on your network setup and what you want your customer experience to be like.
The easiest method to implement would probably be Access Control Lists in the A5.
Add the Client to the list (You will want the Customer IP or probably MAC Address) and set them to deny, Do this for TCP, UDP and if you are feeling extra paranoid, ICMP. Here is a link for a deeper explanation of this system: http://ap.help.mimosa.co/ap-ug-traffic-acl
Another almost as easy route is in the Traffic Shaping Plans in the A5.
Create 2 plans, 1 for your paying customers and 1 for the No-Paying Customers. Then move the various antennas to each plan as you like which then limits the customer. Another Link for deeper explanation: http://ap.help.mimosa.co/ap-ug-traffic-shaping-plans and the client settings http://ap.help.mimosa.co/ap-ug-clients-client-settings-240
Other options are network dependent and are more complicated, but give you options that are not available in the first two systems.
If you have a Radius Network then then 2.4.0 and later firmware let you use that for your traffic control, I don’t know much about it because we don’t use Radius. http://ap.help.mimosa.co/ap-ug-wireless-ssid240
If you know how to do VLAN stuff you can put people into “time out” with CPE Data VLAN: http://ap.help.mimosa.co/ap-ug-wireless-ssid240 and http://ap.help.mimosa.co/ap-ug-clients-client-settings-240 This allows you to do a warning page for those customers.
Where I work we do all of our bandwidth limiting in our Mikrotik routers that we have in each of our towers. This allows us to not have to remember who is connected where and gives us finer control of how we do bandwidth limiting and bursting. But this is a preference and one that many other people do not follow, there are reasons for doing it both ways.