Also just commenting this for others that might want to use shaders with this, as it took me a bit to figure out --
if is_talking: # Apply the talking transformation
trans.shader = "outline"
else: # Apply the not-talking transformation
trans.shader = None
Likely you will need to make a copy of the shader you're using with uniform variables, instead of them being set through a transform. This means you're stuck with one preset (unless you make it a variable potentially?), but it works like a charm!