Once you run the animation assistant for Exponential Scale, the keyframes are locked down and if you need to change the start or end values, you have to delete all the intermediate keframes and re-run the animation assistant. Here is a way to replicate the Exponential Scale via expression.

Great preset for designing in a "Golden Ratio"

It's a small, very simple plugin which replaces textures by using a UV map (like maltaannon's youveelizer, but with much fewer features)

Exports the selected layers and cameras within the work area to Maya, 3ds Max, or Lightwave.

This script creates one new layer for each selected layer in the active comp. Each layer contains an arrow that gives velocity feedback.

This script scales the selected layers within the active comp.

This script scales the active comp and all the layers within it.

Squash and Stretch. Simulate a cube of jello being dropped on a floor.

Time for a Stretch: This expression makes your layer move like gelatin.