APM Pool assign based on host header or URL path

Thank you very much. I assume i can also do something as follows to use the host ?

'when ACCESS_ACL_ALLOWED {
    switch -glob [string tolower [HTTP::uri]] {
        "ww1.*.com/*" {
            app1_pool
            WEBSSO::select app2_sso
        }
        "www2.*.com/*" {
            app2_pool
            WEBSSO::select app2_sso
        }
        default {
            default_pool
            WEBSSO::disable
        }
    }
}'

I notice that this is run on ACCESS_ACL_ALLOWED and i assume this means at the end of the policy being complete. Does this replace the resource assign action in the policy ? If so would there be any way to make something like this run after the user has logged and just create a session variable which could be used in a branching decision later on in the policy ? I'd rather use the VPE to assign rescources (if possible)

If I could create a session variable as part of an iRule it appears to me that the branching rules with in the VPE are quite limited. For example i can't see any way to use a session variable in a Branch rule. Any idea on if and how i can do that ?

Thanks again