@chris@mastodon.chriswiegman.com IIRC you can't change the domain. Mastodon's identity is locked to the domain name.
When I decided to 'commit' to Mastodon I went through a similar process and ended up changing domains as part of that.
What you can do though is treat it as your user moving from one instance to another. Your follows and follower can be migrated to the new server and you can leave a "bread crumb" trail behind for your followers if you leave the old domain up and running. I did this and left the old server running for a month or so IIRC.
You can't migrate your past posts, and I think this is a functionality that most people would like when migrating. It could effectively 'solve' the changing the domain name thing.
I can't remember, perhaps it was snac or pelorma that had a migration script that migrated everything including posts. This could work but then you would be on a different platform from Mastodon. That may or may not matter to you. For me I'm content to stay with Mastodon for now as I expect there will be 'new and exciting' federation features in the future that other apps may find difficulty implementing.
I suppose you could hack together your own posts migration script. I have no idea how complicated the schema is to tease out how to do it though.
HTH