I managed to change the port in runtime by utilizing these 2 console commands:
To start server with any port number: open:9999/Game/Folder/Folder/MapName?listen
To connect to this server: open X.X.X.X:9999
/Game/Folder/Folder/MapName - path to your level file, always starting with “/Game” that is basically the “Content” folder in the editor
9999 - not necessarily this one, but any port number