The Question is: If I would install the famous App "Tincore Keymapper" as a System App... will It get the required root permissions without my Phone being Rootet or damaged? And If the answer is positive: How to Do that via Adb?
If your phone isn't rooted, then none of the apps can get root access, regardless of whether they are installed as system app. Also, I quite doubt how you can install extra system apps without root. Rooting may require a custom recovery and may not be easily done with only ADB.