Is it possible to use proxies to change ports in this way? [closed]

Though not completly the answer you were asking for - AFAIK minecraft can use SRV dns records to alter the default port in a transparent way, I believe you can use it to run the server on a custom port and not having issue with typing the port in minecraft clients each time. You can also use it to run multiple world on the same IP and connect to each by using a different fqdn. the records looks like this :

_minecraft._tcp.name TTL class SRV priority weight port target

in the link below you also have some examples, I'm sure that with enough fiddling you will get it to work https://www.mcmiddleearth.com/community/wiki/setting-up-a-srv-record/