I don't understand the question. You can set the acceleration with an action. What doesn't work? Or what happened and what did you want to happen?
You can limit the max speed with clamp like this:
-> Sprite: Set Path Speed to clamp(Sprite[PathMovement].GetSpeed, 0, 'maxSpeed').
Also keep in mind that acceleration is directional. Positive acceleration accelerates toward the end of the path, and negative toward the beginning.