ok, so I have looked into this a bit more and have changed some of the logic in the ModuleScheduler module. It now listens to notifications. Now, via the remote module I am able to trigger changes to the CSS, so I have added a gradient for BackgroundSlideshow to be able to dim the background images (like you might know that from different websites.

With something like:
http://192.168.22.238:8080/api/notification/CSS_change?target=MMM-BackgroundSlideshow&dimLevel=0.75&apiKey=banana

we are now able to control all of that.
Will further test and then share.

chrga