If you check out the second to last screenshot 'UserPermissions.png', I believe you'd just set the "View username history" to Allow
for your registered users group, and leave "Change username" as Not Set
You may want to communicate to your admins about the "Change Username" page under the admin cp "Tools" tab. I think they'd need to use this tool so that the username change gets added to the member's profile, but I'm not 100% sure. Since installing this addon on my own forum I haven't tried changing a username via the regular admin cp edit user area.