Never

Your login username cannot be changed.

Only the account owner (that's YOU) can see it anyway, so why care what it is?

I just typed a random username when registering for Steam back then, and now I'm not really satisfied with it. 😐 Well, if it can't be changed, then never mind.

Unfortunately, it's an issue with how the database was setup, and was discovered years ago when they tried to implement such a feature.

The last official word we have from Valve is that they are unable to offer account name change as a feature because they cannot get all the issues with ownership verification resolved; you wouldn't want hackers to rename an account so the original owner can NEVER reclaim it. They were working on resolving the Steam database stuff years ago and it is quite possible they figured that out. From what it sounds, it's not likely they're going to get a solution in play any time soon.

Well the only ones who can give a definitive answer on that is probably support

引用自 William Shakesman：

From what it sounds, it's not likely they're going to get a solution in play any time soon.

Or that such a solution will be easily accessible to the general public. They probably want to add friction to avoid people wanting to change their usernames as they change underwear because reasons.