Currently, the only way to change a user name would be to create a different account number, like what happens when an account is bundled with a telephone company, or unbundled. In both cases, the account number "changes," at which point a new login is required to tether the new account number to dishnetwork.com . The old account would show "closed" (old account number no longer active) when logging in under the old login.
There was a point at which DISH was requiring an email address to login, and they diverted the user name to the email address on file (which sounds to me like what happened in your case, Jacob). Interestingly enough, I have seen plain user names not associated with an email address recently.
To the OP, my suggestion to you would be to have the account holder (you mentioned this was a friends account) email the webmaster and have them change it, if the user name is not taken already. They may be able to do that for you but that would be the only option really.