Modifying an entire animation with motion tweens is not as easy as it used to be.
Here's the best answer you are probably going to get.
Scaling an entire animation that does have Scale X or Scale Y animated.
If you have previously scaled anything in the tween, doing this is applied to the first keyframe and the tween would animate to the earlier scaling (the auto-keyframing feature can be a detriment in this situation, especially when it comes to scaling due to the percentages being reset - for this reason Motion Presets also won’t help). In this situation, I recommend scaling using the Motion editor:
1. Go to the Scale X and Y properties in the Motion Editor.
2. Press the Alt key while dragging the curve in each graph up and down. This scales the entire scale animation at the same time (same as edit multiple keyframes).
3. If you need to proportionally scale the motion path for the tween as well, select the path on the Stage and use Free Transform or enter a new value in the Transform panel.
I have had success with the above method, but from what I can tell you can only do one property at a time on one object at a time. So it is an awful amount of work.
As for step 2: while dragging the whole curve it seems the property value is very reluctant to snap to whole integers and I often see values like 200.35%.
Same thing applies for dragging property keyframes up and down in the motion editor. Is there a way to get nice clean numbers? I I want to scale something by 50% I don't want 49.83% I find myself often keying in these values by hand.
For me even though scale X and scale Y are "linked / locked / contstrained" It seems I get mixed results with this feature. Changing scaleX doesn't always change scaleY