Since Trello's merge with Atlassian I can no longer find the option to change my initials that's visible in Trello. I am using Trello with one who have the same initials as I have. Would be nice to be able to change this, since you can't tell any difference between us. Now the only option seems to be to change full name.
That's true. You can only change your username to a name that is not in use by another user.
For more information :
https://help.trello.com/article/728-changing-your-username