How to change AnimationClip KeyFrame values at runtime

Hey guys,

is it possible to change keyframe values from a clip at runtime via script? (non-legacy) I want to change the value of the "Body > arm" - rotation.z. There are 3 keyframes at the normal clip and i want to change the only the 2nd keyframe value to maybe 120f.

At the Screenshot below you can see my "RightArm" Property (first keyframe value is 0). The result have to be, when i rise my mouse (position.y is maybe also 120), the arm has to follow while hes in this animationclip.

I hope i descriped my problem enough, that you can understand it. Every google solution and many code examples doesnt work...

Thanks!

Unity: 2019.2.8