Whether it is possible to enter a group in which there are no people, for example, after leaving it. And in the map editor, make buildings in advance and assign them a group, and in the game enter this empty group.

Wow, I'm confused. Are you sure you wrote it for this mod? I assume, by "group" you meant "force" (team), but I don't understand the last sentence. It seems like you struggle to change force in the interface of the map editor.

Oh sorry for my english =))How do you join a group without a single person in it?There was a case when I left the group and the buildings became hostile, but I could not return to the group {{{(>_<)}}}

There are other mods for interactions with forces. (you can use PvP scenario instead)

I have https://mods.factorio.com/mod/BTeams but it's not fully ready.

very good mod （￣︶￣）↗