From what I understand due to the way that Lemmy handles federation, it doesn't (currently?) have a way to handle an instance changing its domain name and still being able to communicate or even an individual user changing their instance and retaining their comments/votes/etc... (this might be more ActivityPub limited since the way Mastodon does it still seems pretty hacky and just a work around for underlying issues).

From a website perspective, yeah, just change some settings and you're good to go and accessible on the web, but that doesn't mean that anything regarding Lemmy is going to actually work.