update existing users' email only

I have uploaded users and their emails using the module. However, due to a change in domain name etc, I now want to update their email addresses only using this module. The UserIDs are still the same, so I want to use UID as key.

Please confirm if this can be done. I tried it out but it duplicates the users, so unless I selected the wrong options.

If not, please is there a patch for this? Thanks