Edit: Interesting. It looks at first glance like maybe they only have the ability to edit posts as seen by local users on lemmy.ml (which actually makes sense -- I would think that part of ActivityPub is verifying that content that supposedly comes from some particular user actually comes from that user). Personally, admins on a server feeling that they have the right to edit their user's posts for any reason would lead quickly to me exiting that server, but that's just me.