The CSS does not have any QoS feature on it, since it is meant just to balance the traffic. Anyway there are some other setting you my like interesting.
To limit the usage of a service, you can configure max connections on a content rule, so if that value is surpassed, the service will stop receiving new connections and will work with the existing connections. To configure this use the following:
CSS11503A(config-service[https])# max connections (Range: 6-65534) .
Pretty much that command is the only way to control traffic being sent to a specific Service.
Another choice is to create an ACL to redirect the traffic form an specific user or network to a determinate content rule or service, and this way avoid the CSS to process the traffic from that user/network as new saving some resources.
