[John James Jacoby]

Well, you’d have to go poking around with phpMyAdmin, and change the users table and the usermeta table to match. This will prove difficult because the information is serialized in such a way as to make it difficult to read with the naked eye.

Will it cause a problem? In my OCD opinion, anything that isn’t meant to be that way can pose a problem later. How many users are affected by this issue? Can you delete them, reset the last ID in that table using phpMyAdmin, and ask them to re-register?