This is a suggestion directly to the devs for a way they could allow modders to add things to the Siptah map without risking the DLC’s content being released.
Perhaps a method of adding things to the Siptah map could be devised where the game reads a file that has nothing but coordinates and listings of what to spawn where instead of the actual map file. The editor would need to have a map showing, but it wouldn’t necessarily have to be the actual map file. It could be a simplified terrain with straight up blocks (i.e. literally this) showing where things like buildings are already placed, and if the modder wants to remove them, the coordinate file would recognize that and make them not spawn in on the map if the mod is enabled.