-s-
you actually can change your username. you just have to go to "edit profile" and if you delete your current username in the provided space, you can put in a new one.
Ignore User
Both you and this user will be prevented from:
Messaging each other
Commenting on each other's stories
Dedicating stories to each other
Following and tagging each other
Note: You will still be able to view each other's stories.