Quaternion rotation?

Hello. How do i rotate animated bone with quaternion keyframes 180 degrees using graph editor? I have character animation (from mixamo) and I want it played 180 degrees on z-axis (world) from it’s initial orientation , i need to turn character to merge animation with existing one. I don’t get how to do this simple task using quaternion rotation when i select keyframes in graph editor and move them up\or down character turned less than 180 degrees and won’t rotating further.
I would prefer to work with euler but keyframs are quaternion and i have to deal with them. Tho quaternion rotation logic is beyond my understanding.

To achieve needed result i’ve made additional bone to armature as parent to hip bone, and added one keyframe to new bone rotated whole character to 180 degrees. Maybe it will help someone.