insert field to HTTP header

When you do this the logic will be

If client ip address equals 10.0.0.0/16 then insert or if the port = 80 then redirect, else go to pool.

It sounds like you need it to get past the first IF statement, before it checks the port, which is what your example wouldn't do.

In that case perhaps you might want to do it the following:

when HTTP_REQUEST {
if { [IP::addr 10.0.0.0/16 eq [IP::client_addr]] } { 
    HTTP::header insert STRING MLint 
    if { [TCP::local_port eq "80" } {
         HTTP::redirect "https://[HTTP::host][HTTP::uri]"
    } else {
    pool eRoom-Servers-Pool
    }
   }
}

Hope that helps

/CB