Do you have any external references to any commits that matter, for example in your communication platforms (emails, Slack) or your bug tracker? Or, worse yet, in places where they aren't just text format references, but used for things like CI/CD caching decisions or security scans?

Once you rehash the entire repo, every single one of those external references will be broken. Because no, there's no support for looking up old hash -> new hash or the reverse.

I think I remember something for this for mercurial to git migrations, I hope when its git 2 to 3 something similar is made (or it will take some time to adapt like when python did its 2 to 3 migration).