iRule size limitation

Write a new iRule where you use Data Group.

ltm data-group internal data_www.someapp.com_sourceIP_destPort_pairs {
    records {
        10.10.10.11/32 {
            data 10001
        }
        10.10.10.12/32 {
            data 10002
        }
    }
    type ip
}

iRule:

when CLIENT_ACCEPTED {

      if { [class match [IP::client_addr] equals data_www.someapp.com_sourceIP_destPort_pairs] }{
        node 10.55.55.55 [class match -value [IP::client_addr] equals data_www.someapp.com_sourceIP_destPort_pairs]
      }
}

Thats all you need, and it will achieve the same results of your 65k digit Switch-Monster.