I tried that but for whatever reason the blueprint class I have in the project doesn’t let me edit the instance array on the actor in the scene at all (This also seems like a bug, I can add instances from the blueprint editor but can’t add or edit any instances once it’s placed in the level. Should I open another question about this?).
I was, however, able to test it by dropping an empty actor into the scene and adding an InstancedStaticMeshComponent into that one. If I change or add an instance on that actor (using the details panel, not a blueprint) during simulation and try to save its changed properties it still says no properties were changed.