TBH I've been an admin/mod in several forums over my life and I always hated the idea of changing usernames in the first place
^^ This, usually. It's worse when they start using a new set of graphics to go with their "new persona". To be fair however, I can also remember picking a really stupid username and being glad I could change it. shudders
For example, I am using the module nodebb-plugin-custom-pages and created a page called home.tpl and route /home, now if I change home page to a custom url /home and navigate to home page, it opens up /home but it is still visible in url. While setting it up to popular, /popular does not show up in url.