Is there any way to change a local user to a global user?

Is there any way to change the local user in sub wikis to global user in global wiki? Except re-register.

A user is nothing more than its profile page. You could simply move that page to main wiki. Don’t forget to then put this user in the right groups in the main wiki (like XWikiAllGroups).

But keep in mind that you will break any link to this user (page authors, etc.).

Thanks a lot!