Mastodon has a feature to move accounts from one instance to another instance. I spent some time recently exploring how this works so that we could support it in Micro.blog. I used this to consolidate my ActivityPub presence from multiple Mastodon accounts to just @email@example.com, powered by my blog and Micro.blog. From what I can tell, this feature is not well-documented. It does not exist in the ActivityPub spec. The “Move” activity examples in the companion ActivityStreams spec also do not cover moving accounts.