Overriding animation's bone transform?

I am trying to figure out a way to override a bone’s default transform when animations play. I want to use it for making adjustable body parts like arm length, leg length, torso length, etc. Let’s say I want to make the legs 2x as long then I want the bones to stay like that during the animations so it’s 2x as long when animated.

The problem is I don’t understand how to go about this or if it’s even possible because I know that animations work by storing bone positions and rotations. I know I could make multiple animations with various bone positions, but then I’d be limited to certain sizes and I would have to make multiple versions of every animation. I want something I can adjust to any degree to use with a slider kind of adjustment so not set lengths like 1x, 2x, 3x but everything from 1x-3x.

Is there a way to change the bone’s position inside the animation itself or to add some kind of modifier that “adjusts” things during each frame?

EDIT: This is an example of what I want to try to achieve. Note how you can change the neck length, arm length, leg length, overall height and the animations 100% adjust according to the new bone structure.

You can freely change a bone’s transform in Lateupdate(). This will make sure that it gets applied after any animations are played.