Change the Default UI Material?

Is it possible to change the default UI material to use a different shader? Or is the only way to specify an override material for every Graphic in the scene?

I'd like to experiment with adjusting the UI-Default shader, but I can't find a way to easily apply the modified version of the shader to all UI elements in the scene.

I was hoping there'd be a "Graphic Settings > Default UI Material" field or script call somewhere. Graphic.defaultGraphicMaterial seemed promising, but it's read only....

Change the Default UI Material?