Changing destination pool TCP port via iRules

Please try Colin's suggestion with your rule:

when CLIENT_ACCEPTED {
  set dport [TCP::local_port]
  if { [lsearch $dport [list 12005]] != -1 } {
    TCP::collect 1
    return
  }
}
when CLIENT_DATA {
  if { [TCP::payload] contains "myData" } {
     set new_port 12007
  }
  TCP::release
}
when LB_SELECTED {
  LB::reselect pool [LB::server pool] member [LB::server addr] $new_port
}

This should cause the load-balancing engine to pick a pool member as normal, but then override the port/service with the one you want.

We'll have to think about your suggestion.