I'm not sure I completely understand what you're after, but importing & exporting composite shots might help you.It sounds like you're wanting to create a 3D shape out of various planes (e.g. a cube), and then reuse that multiple times? If so, or if your problem is similar to that, then you can right-click the composite shot in the Media panel and choose 'Save As'.This lets you save the composite shot to an .hfcs file. Then later, in the same or a different project, you can import that .hfcs file by clicking the arrow next to the Import button (again in the Media panel) and choosing 'Composite Shot' from the popup menu.
Is there some way to only react with the "visible background" or importing a certain file type so this might work? Or some way of adjusting the bounding area so that the "deflector" area can be customized?
Furthermore, I've noticed that when particles are reacting near the edge of a deflector, depending on the texture, it may extend beyond the deflector boundary. Is there any way to control this so that the texture doesn't extend beyond the deflector?
Not at the moment, the only way you can achieve this is by "puzzling" the shape out of multiple small rectangular planes, I guess.
That is also a technical restriction, because the collision detection doesn't work based on the texture but the center of the particle... Maybe we'll see improvements here in future version, would indeed be a good detail improvement.