irule to change http host based on port

Try this:

when HTTP_REQUEST {
   if { ([HTTP::host] eq "server.domain.co.uk") } {
        switch [TCP::local_port] {
            443 {
                HTTP::host "server-443.domain.com"
                pool POOL_443
            }
            444 {
                HTTP::host "server-444.domain.com"
                pool POOL_444
            }
            446 {
                HTTP::host "server-446.domain.com"
                pool POOL_446
            }
            447 {
                HTTP::host "server-447.domain.com"
                pool POOL_447
            }
        }
    }
}

or even better

when HTTP_REQUEST {
   if { ([HTTP::host] eq "server.domain.co.uk") } {
        HTTP::host "server-[TCP::local_port].domain.com"
        pool POOL_[TCP::local_port]
    }
}