When you want to create a slave site from the front-end, you have to specify a "website template" that will be used for the replication.
In the "Website template", you can specify which user will be proposed to the front-end user as the administrator.
So create a special user in the website that is used for the replication and give it a privilege as administrator (not Super Admin).
When you are the "website template", you will have the list of user and select the one that you have specially created to be the administrator for a slave site.
When you create a slave site from the front-end, the login name used as administrator is displayed to the user. This is the one that you have selected in the "Website template".
This is this user that will have its email and password modified by the front-end user.