Change curve

This is an exercise that is based on chameleons tongue movement. 

First,

I create a series of 4point surfaces to imitate chameleons lower jaw.

Then,

I generated an Interpolate curve, defined by 3 points... This is the curve that describes one way of the tongue´s "path".

Next,

I associated this Interpolate curve with a Graphmapper, generating a curve that also has a way back movement.

The thing is that the way back movement is not the same as the initial movement. 

I´m having difficulty in the way back movement of the tongue.

My question is:

How can I generate with an a slider, that when the curve after it reaches it maximum extension point (also maximum point in the graphmapper), change to another curve, way back movement

ps: I attached the Rhino and grasshopper archives