To clone the Platform Manager role to allow users to view/change usernames:

1. Navigate to Core
2. Select Security > Roles. 
3. Click Add in the upper right page
4. Give the clone role a name and select "Platform Manager" as the base role, then click Next.
5. Check the Tasks on the right-hand side and mark the role tasks listed below, then click Next:
  • User Name Format
  • Edit User Profile Data
  • Main Profile Field 
  • Profile Field
6. Search the user and click on the blue-link arrows to add the user into the Added Users section
7. Click Save and Exit 
Note: The user with the clone role with above listed role tasks will be able to change everything in the profile - not just the username.