I think it’s more or less as you describe. I think what OP is suggesting would be more like a way to migrate a community. Export everything from !example@oldserver.ded and import everything to !example@newserver.liv

I think something like this exists for Mastodon users, but I’ve never played with it. You could use this to migrate communities from an instance that was going down or otherwise no longer suitable. Even if all old conversations are “frozen” or locked, it would still be useful upon occasion.