Resolume outputs the pixel data based on the video played, so changing the video opacity, or the colors with effects would probably do this in software.
I do currently do that for on the fly adjustments as a whole. The purpose behind having a lumiverse or fixture assignment of this would be to calibrate it on the fly to the other lights. The colorspace for each light can be drastically different and may not be apparent until a certain video or color palette is running on them. This kind of post processing is then able to compensate for that. A simple example would be pulling magenta out of specific lights on the map but not the whole video. Or just dimming those down compared to the rest. While you can do that within the advanced output, it's not dynamic. I can't boost those back up for the next clip or later in a show/project.
I am probably more sensitive to this than most as all my projects are filmed and I have to deal with how it ends up recorded and seen a thousand more times.