When we change user login/email info...it erases all of the user's data/couses/history?

Content

We are changing our email login/username login at our company.

Here's what I've done so far:

1. I am downloading all of our users to an Excel document
2. Performing a Find and Replace in Excel
3. Replacing the older email addresses/usernames with the new version
4. Copying and pasting new information into Taleo User Bulk Import

However, when we do a bulk import with the new username/login info it overwrites all of the user's previous data/courses/history. I would prefer to do a bulk username/email change versus having to edit each individual user account with the new email/username login credentials.