Is there a way to have a 'none' material that is visible in the editor but not when playing?

I am creating a world (buildings, tunnels, etc.) from modular pieces such as static meshes or levels for more complex sections. In many of these pieces, there is clearly an outside part that should never be visible. This is obviously true for tunnels, but also e.g. building parts that are constructed using “inside rooms” and “outside walls”, usually connected by door frames and windows hiding any potential gaps.

I guess one could use meshes that simply don’t have the other side at all, but I find these are more difficult to work with in the Unreal editor.

I would love to have some kind of ‘none’ material to not make it draw triangles from the parts that should never be visible. For performance. I do not think visibility checks will work here in general as the inside part of the meshes could still be visible. It would also be great in the editor when setting up the world to see proper physical bounds of the object and to highlight any gaps in placement.

I have thought about setting up super simple ‘M_None’ myself with just maybe a static color. But are there performance downside to having one more material slot in the majority of static meshes? I’m not an expert on shaders and that but I guess it has to do more shader switches. Also, I assume these fragments are still being rendered in the end.

Google didn’t quite help me here but it might be that I don’t know the right keywords.

Another option would be placing a customized bounding box in the level whenever the object is selected in the editor. Then you don’t need to alter every mesh for editor setup purposes.

Would be something like overriding the actor selected / unselected in editor events which I haven’t ever done but I would assume exist…

Thank you, I will consider that. Probably this all is a matter of premature optimization but this feature feels like it would be very useful for me.