Hi @Daniel the key thing to consider about their learning history, is that the merge function can only transfer course enrollments.
It does not transfer enrollments in Learning Plans - so depending on how much your site depends on Learning Plans, people may get confused after the merge, as they will need to re-enroll themselves into learning plans to get back to where they were before the merge.
Also, if they have a history of viewing assets in Coach&Share channels, creating playlists, commenting, or asking Questions to Experts - those won’t be transferred using merge.
In your scenario, my approach would be to rather change their usernames/emails on their existing accounts instead of creating a new account and merging data. In that way a full history of their actions, learning plans, comments, etc. will be preserved and available to them after the change. Also, from the reporting perspective, data will be more consistent (you won’t artificially inflate the number of users).