It’s been a long time since I had done this and I was performing a testing and evaluation at this time.
I have not pursued this further yet as I have had not need to just yet. Had quick look to find the code I did to do this and could not find it. Will have to get back when/if I do as I will one day get back to this. I could have mistakenly deleted it while performing some cleaning.
As far as spawning objects in this new world persistent level, it was done in code and not through the editor as one cannot create a new world and display it in the editor as I remember. And as I remember, everything was in back and white and very dark as only a single point light source was used.
As I said, this was done as a test only.
I hope this helps.