You can animate Material Room settings by clicking on the key icon next to whatever parameter you want to animate.
A new dial will be created in the Figure's Body or the Prop for that value, which you can then animate as you would any other value.

Adding (or removing) nodes during animation may be anywhere from very tricky to impossible.
One way to get the same effect is to setup two Shader networks, feed them in to a Blender node, and drive the Blend_value using the appropriately modified output from a Frame_number node.