It's easy to change resolution ingame but you have also another render problems like context UI in Select Server and Select Character.
If you try to change the resolution ingame, you will see that when you switch to select server or select character scene, the UI isn't adapted to the new resolution.
Also another problem is the chat. When you tip letters in the chat with a different resolution than the original, the letters won't show right in the chat but when you press enter again to send the chat text works fine.
If someone wants to help fixing this would be great :D