Hi I am trying to add effects (like fade) to the visualizer, but I'm not sure how to that. Or is this not possible at the moment?

Any help would be great.

for "visualizer" you are referring to master effects? like AUDIO SPECTRUM FILTER and AUDIO WAVE?
if yes... right now i think you need to render the project and make a new one importing the generated CLIP and apllying effects on it.