WPF - Changing Animation Path

Question

I have a MatrixAnimationUsingPath that animates an arrow moving along a path... In my code behind within the MainWindow I am setting the PathGeometry to a given PathGeometry.

This works fine and when everything loads the arrow is moving along the path fine... But when the user clicks a button - in the button handler I need to change the PathGeometry to a different Path - the change in path doesn't do anything...

How do I make it so that I can set the Path of a MatrixAnimationUsingPath then change that path at some given point in time???

Note at the moment the arrow just keeps moving along the same path regardless of what change I make to PathGeometry.