Unfortunately it is not possible to appeal usernames on AKO as the portal no longer provides several options for usernames. Rather, the system generates a username based on the definitive personnel database user information is pulled from when you request an account or a username change. There are only two reasons a username can be changed: if the username is not EUN (Enterprise UserName) compliant, or if it is not the user’s legal name according to the data record in DEERS (Defense Enrollment Eligibility System).
For more information on usernames, you can follow this link:
Account: Username Guidance(32).
The AKO/DKO Username Policy can be found with the AKO Policies page, and you can click on the following link to bring up the policy: https://www.us.army.mil/suite/doc/13359518
AKO/DKO pulls its username guidance from Army Regulations.