How much control/access does my instance owner haver over my account? - lemy

I noticed that there were some accounts that were hijacked by the instance owners. All the posts from that user were then edited to say what happened. This kind of surprised me, I figured instances could delete posts, but not edit them. So how much control do they have? I assume they can’t see my password (hopefully). Can they post in my name? Do they have all the access to my posts to foreign instances that they do over local posts?