No official solution or answer, so nope. But it gave me an idea to build my own (slimmed down) version based in the shown stuff, which boils down to a simple actor with Instanced Static mesh components, and some structs, that can hold some relevant data for each ISM component and each instance.
The idea was to get an instances ID and use this ID to look into the struct for this ISM component to find whatever data is stored there. F.e. if its a placeholder for an actor, or if it has health points or of it should do damage etc. If it was a placeholder for an actor, then you could always replace this instance with such an actor and vice versa. I thought, that most of the time i maybe don´t need to spawn in the real actors all the time, if i just want infos for current health points.