What happens, when you have to move your Mastodon account to another instance?

1 Feb fedimeister.onyxbits.de
They say, it doesn't matter which Mastodon instance you sign up with. You can still communicate with the entire Fediverse and when push comes to shove, you can also always move. Well, push came to shove for me and I had to move. So let's talk about the giant asterisk that belongs after both of those claims.