Link to see the face in action on youtube (it's the official tv spot channel, please don't make personal comments there).For some reason the link to the animated gif is not working and I haven't a backup)
AS has as a way of work that sometimes can be a limitation: any draw you made on it, will be always present on the whole animation. You can, of course, hide layers, turn fills transparent or simply put the shape off of the screen, etc, but the construction curves will be always on the animation.
Well, we can take advantage of that behavior. check this gif:

(I just found a backup

It has several curves which width is zero until you want to show them. This way you can make several expressions and add or remove lines depending of what you want.
Check the anme file. It has each expression on an action (to use blend morph). Takes some time to construct it, but works like a charm for long projects.
PD: the character has hair, ears and body. sadly I'm not allowed to share the whole character now, so I reduced to the minimal.