Sure thing, just press CTRL + V
That does not work on the server side of things. Stop the container and then you have to go in the main directory from the game server and there you will find a file called "serverconfig.txt", open it up and search for this line and edit it:
Save the file and start the container again.
That's pretty nomal since you only edit the port number in the template, you have to go again in the game directory and edit the "serverconfig.txt", of course I would recommend that you first stop the container and then search for this line and edit it:
Save the file, then go to your container template, remove the entry for the port number, click on "Add another Path, Port, Variable, Label or Device" from the drop down select "Port" at Container and Host Port set it to both the same number that you've entered in the "serveconfig.txt" file like this:
Click on "Add" and "Apply" in the template now you should be able to connect to port number 7778.