Legacy systems only support REF linking on port 20001. Be aware that some repeater owners will block incoming link requests. If you're have problems linking, make sure the IP address is correct first, then check with the repeater owner.
You just need to edit your gwys.txt file in your QnetGateway build directory. Then you can either use ./qnadmin to restart (actually stop and then start) qnlink, or transmit an "_ _ _ _ _ _ _ F" to your hotspot. You could also use qnremote. This is how I would ask my hotspot operating on channel B to reread the gateways file: qnremote b n7tae f. Qnremote will take care of converting to uppercase and right shifting the "f" before sending it to your hotspot.
It can sometimes take tens seconds to complete the rereading task if you have enabled legacy linking authorization in ./qnconfig. This is because auth.dstargateway.org can be very sluggish at times. Also, please be aware that auth.dstargateway.org is a round robin server and will connect you to one of a number of different authorization servers. Each of these severs can return different lists of reflectors and repeaters, so it's a best practice to do what Elmer is doing by added desired nodes to his gwys.txt file manually.