This has nothing to do with the version of Wii U, simply the fact that TCP Gecko is designed to re-launch when Mii Maker is opened again. This is because TCP Gecko is a backround process running app, if you were to open Homebrew to re-launch it then the console would crash - solution? Replace Mii Maker for relaunching if the TCP Handler crashes, so you don't have to reboot the console everytime.
What type of codes? Because if you're referring to the use of a custom keyboard in Mii Maker this is done via replacing the
swkbd.rpl file which holds the keyboard contents