IRULE redirection to maintenance pool based on client IP and cookie...

I think this will do what you need...

when HTTP_REQUEST {
    if {[class match [HTTP::header "True-Client-IP"] equals MAINTENANCE-CLIENTS]} {
         if {[HTTP::cookie exists "MAINTENANCE"]} {
             switch -glob [string tolower [HTTP::uri]] {
                 "/site1*" -
                 "/site2*" -
                 "/site3*" { pool MAINT-A; persist cookie }
             }
              go no further
             return
         }
    }
    switch -glob [string tolower [HTTP::uri]] {
        "/site1*" { pool POOL-A; persist cookie }
        "/site2*" { pool POOL-B ; persist cookie }
        "/site3*" { pool POOL-C; persist cookie }
    }
}