I read most of the thread, but I miss a FULL explanation of how to install/replace that files, and how to do it exactly. I could search for that info in the whole thread, but why don't anyone write a little FAQ on how to implement the files exactly. There are several questions that I can not find an anwer to. Like: Do I really have to use an FTP to install this, or may I just insert the files on the WiiU itself, because most of the Games are saved in the NAND? Could anyone wirte a little "How to..." to it?
Yes, you need to use an FTP application. AFAIK there doesn't exist a homebrew application for managing files on the console itself, you can't access the Wii U's internal NAND storage from your computer and the Wii U USB format isn't readable if you unplugged it from the console to try to access on a computer. Your other option would be to load games from the SD card using Loadiine, in which case they will have been extracted and you can access / edit the files by plugging the SD card into your computer.
I have used FTPiiU Everywhere (vs FTPiiU, which cannot access the NAND or USB, only the SD card, so the only advantage is not having to shut down the console to eject the SD), but https://github.com/Laf111/WiiUFtpServer is better, as FTPiiU Everywhere has some problems with setting file permissions correctly.
AIUI the process will be the same for each. https://wiiubrew.org/wiki/FTPiiU describes the basics:
Download FTPiiU using the links above, and unzip the files inside to sd:/wiiu/apps/ftpiiu. You can also download it using the Homebrew App Store. Once this is complete, you will be able to see the program inside the Homebrew Launcher.
Once you launch the program, you will be given an IP Address and port to connect to. Use your favourite FTP client to do so.
Once you have opened the server application on the Wii U and connected to the address it shows with the FTP client on the computer, you can copy files between your computer and the various drives on the Wii U - the main ones you will need are storage_usb for games on an external hard disc, and storage_mlc for games on the NAND.
The page about whatever you're trying to edit will hopefully tell you which folder to look in e.g. saxoman1's post here: https://gbatemp.net/threads/new-to-wii-u-homebrew-a-question-about-virtual-consoles.465095/page-2
If you have a specific question, I am happy to try to answer it.