Challenge Requirements
Create a new user with the following settings:
Profile: System Administrator
User License: Salesforce
Username: Must include guestadmin somewhere in it
The new user must be inactive

I created the new user with all the requeriments, but I mistaken typing guestadmin in the username, and when I try to edit user to correct the username I get:

Error: Please do not change usernames in the Trailhead Playground.

How can I change the username to validate the challenge?