In fact, I can't name a single service I've ever used (ever!) that lets me change my username.
In fact, I can't name a single service I've ever used (ever!) that lets me change my username.
People transition and might not want a username based on their deadname. People get married or divorced and change their legal name, which can have ramifications on their usernames. People might just get older, and lose significance of old pseudonyms.
of course it can be used for abuse - so show the old values next to it / on their user page / etc. allow N changes / limit the frequency. etc.
this would remove one of the reasons cited: "People transition and might not want a username based on their deadname." (People go to great lengths to remove references to their "deadname" and consider any mention of it seriously offensive.)
However, despite my downvotes (-4) I am unconvinced by that argument and the other replies. I don't think it's important to do this at all.
Facebook? Twitter? Instagram? Any of the phone-number-based social apps (which have a poorer UX because of it, but still all allow changing usernames seeing as phone numbers change)? Also I believe Skype does allow changing usernames.
Pretty sure you have to pay to do it, but there are definitely services that let you change your user name.