Problem Merging a mesh (I want to replace the instances)

I’m modeling a building, where I’m cloning this windows along the wall. I want to make variations of it so it doesn’t look cloned (windows open, rusty fence, etc) But this windows has at least 12 pieces, some of them will change materials or change the geometry.

The problem I’m having is that when I merge them I get a new mesh, and I can´t update it later.
One way I solved it is grouping all the pieces, but when I clone it I have a ton of elements in my outliner list, so is a nightmare to look for other geometries there.

In other projects I saw some Actors that have various meshes inside, but I can´t figure out how to make it.

Ok, Im working my asset with Blueprints, I have one for the main frame and another for the window. I make variations of the blueprint (open, close, mi open, etc.) and then replace the blueprint with RightClick>Replace selected Actor with:

An it is working for me.

To keep the scene clean, it is possible to have a building in one Level and load it in another? I need to do like other 10 buildings like this in my scene and I have already too many object on scene