If you try to change your username in Domino, you may see the warning "Changing your username can have unintended consequences. Please proceed with caution." (Screenshot below.)
What are these consequences?
The exact consequences can change depending on your Domino version and specifics of your installation, but one of the most obvious consequences is broken links. For example, if you share a project with your colleagues, the URL you share is of the form <MY-DOMINO-DOMAIN>/u/<USERNAME>/<PROJECT-NAME>. After you change your username, the old link will no longer work and you will need to direct your colleagues to the new URL i.e. <MY-DOMINO-DOMAIN>/u/<NEW-USERNAME>/<PROJECT-NAME>
Hope this helps! If you have specific questions or comments about changing usernames, please let us know in the comments.