I'm pretty sure you don't need to update fwauthd.conf unless you are doing some kind of legacy User/Session/Client authentication for FTP. However an FTP service on a non-standard port needs to be set up correctly so the firewall can properly sniff PORT commands and pinhole open the necessary data ports. This is why FTP control connections (port 21) always go F2F (but the data connections can be accelerated by SecureXL). What you should be able to do is clone the existing FTP service, then edit the name and port number like this:
Use this new service explicitly in your Network rules and you should be good to go.
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