Can I export a list of users?

There is no native Concourse feature for this. However, you can visit the Admin > Users page to search for users by name, email, or ID. Only the first hundred matching results will be shown.

In addition, if you are simply looking to review what changes need to be made and are using feed processing to populate the system, you can simply run the user feed again. For each row if no changes are seen, it will ignore it. Otherwise the row will be used to either update the name/email or create the user if the external user ID didn't exist.