How do i redraw an entire curve with the mouse (as opposed to one single keyframe redraw)?

When editing an animation curve in unity curve editor, what happens is that the mouse selects one single keyframe that you can then move around across both x and y axes. This means that you can only modify one single keyframe at a time with one mouse drag.

I would like to: 1- be able to modify keyframes values only across the y axis (up down but no change in position left right) so that the modify key frame keeps its original x axis value no matter what. 2- Be able to drag my mouse pointer across multiple keyframes and have them modify their Y axis values accordingly. In effect redrawing the curve with my mouse pointer as if with virtual a pen.

How could I achieve that? Is there a setting somewhere I can change? Or Should I implement my own curve editor (if yes how?)?

I declare my curve this way:

 public AnimationCurve _pitch;

and I populate it this way:

  int T = 100;
     ks = new Keyframe[T];
     int i = 0;
     while (i < ks.Length)
         {
             ks[i] = new Keyframe(i, Mathf.Sin(2* Mathf.PI/T *i) );
             i++;
         }
     _pitch = new AnimationCurve(ks);