OK, so I've been playing - just in case anyone's wondering, I managed to fix my problem - in a way.
I wanted to create content to put into scenes so that during that scene in the play, I could output the visual that was required.
I used groups....see screenshot below.
Basically, I created groups and named them in Acts and in subsets of scenes and layered the quad content in those scenes.
I set everything to 0% opacity, so that I could bring them up quickly or slowly in my own time and it means that if I have used an effect, I can click the lock to prevent me accidentally using it again. I can do the same with scenes, when I'm done with a scene, or even lock down the first ACT during the interval. If I need to use the same effect in a separate scene or act, I can either drag in a new instance or simps reuse from another scene - making sure I unlock it, too.
I read another thread that said that all the quads had to be reset, as actors moved things around. My solution is to ensure that the actor replaces the object to be projected on back in its original position (mark the floor if need be) rather than the MadMapper tech having to reset the software. If there's any doubt and marking the floor is impractical or undesired, then run the projection and get the actor to replace the object as required to fit the visual.
This looks OK for me, so far. I'll see how things go in rehearsal.