Rotate bones during mecanim animation with generic avatar

Is there a way to specifically control the rotation of a bone via code while using a Generic avatar within mecanim? This was easy with the old animation system, where you would just rotate the bone within LateUpdate. Currently, attempting the same thing results in mecanim always overwriting the adjusted bone rotation regardless of where in the pipeline you rotate ( Update, LateUpdate, FixedUpdate).

I also tried to put in all of my animations with a Skeleton Mask that specifically left out the bone I wanted to rotate. This didn’t seem to make any difference.

You might want to check whether this thread gives an answer to the question reported here:
How to combine mecanim and script based bone movement/animations?