How can I give variation to animation curve in Unity? (Raw mocap data)

I am trying to give subtle variation of animation to Unity avatar animation. Currently, avatar moves exactly to what animation keyframe instructs every time. Animation I am using is Raw Mocap Data for Mecanim by Unity(https://assetstore.unity.com/packages/3d/animations/raw-mocap-data-for-mecanim-5330). I also noticed that Unity interpolates between keys in keyframe to offer "Smooth" movement. However, I would like to programmatically change t$$anonymous$$s smoot$$anonymous$$ng(interpolating) in given time interval so every time it moves, it would be a little bit motion, just as how human moves(The way how when athlete repeatedly "lifts" weights, he moves little bit different for each repeats.).

I tried changing the "Curve" in animation inspector tab but it didn't work.

Also, I tried manually changing the interpolation curve in Animation window curves (curve option between Dopesheet and Curves button). However, it looks like I cannot change them because its Read-only file. How may I change it?

Eventually, I want to make avatar move with certain variation, just like humans do.

Thank you for sharing your time!