Improvement to flow of account registration: Claim username note

[PowerChell]

Users on the internet are very used to being able to change their username to any available username they please. Yet in Source, this is not currently an option. The permanence of their username should be made very clear to them when claiming a username to reduce frustration from users in the future.

All this enhancement needs is a warning/note on the page where someone is claiming their username: NOTE: Due to ___, you will not be able to change your username in the future. Choose wisely!