One of the cool things you can do in Construct is add multiple effects to an object. For example you can add a Warp effect to distort the object, and then apply...
Or to clarify. You use a Blend mode to combine 2 layers. Ie. Source atop or something similar. And want to apply an effect on the combined result. Does not seem to compute.
Layout effects alter the whole display. But to have an effect that only alters a group of layers, e.g. just two layers together, would require sub-layers.