[Dan Hep]

i think the easiest way for you would be to let the script duplicate the layer you are working with and than let it set the in point of the new layer to the out point of the first layer (see code). then you can set a new expression for the new layer.

newLayer: Layer where you want to set “Expo out” or something
theLayer : Layer which already contains an Expression “Expo In”
(you also should set some keyframes)

im using it like this, if there is a better way, i would be happy to hear it.

var newLayer = theLayer.duplicate();
newLayer.inPoint = theLayer.outPoint;

newLayer.property("xRotation").expression= "expression code goes here"