Thank you for your feedback, I am also aware that overriding the RC channels is not the best practice, but I was unable to achieve a rotation over the YAW-axis in any other way, so this was my last option left. As you say, I also believe that "taking over the stick" has more disadvantages, than advantages, indeed.
The drone is wobbly / unstable in any circumstances and I have managed to keep the rotation working when overriding the RC channels (I dont know why it stopped working for a little while). Although if you have any other suggestion on how to achieve a rotation over the YAW-axis without overriding the RC channels, I would be happy to try them.
Talking about GPS injection, I still did not discover how to do this, I am only 2-3 weeks familiar with these technologies. However, GPS injection is something I would like to do because it is needed for my project to succeed. The goal is to fly to a given GPS coordinate and avoiding obstacles on its way.