Hello,
well unfortunately, the powershell cmdlets do not take a user account as a parameter. What you can do is something like the following:
1. Go to the charms on the right hand side by hovering the mouse all the way to right hand corners or push Windows Key + C.
2. Click on settings | More PC Settings
3. Under your account click on Connect. Specify some live or hotmail account etc.
4. after you Finish the above process, go back to powershell and type in Show-WindowsDeveloperLicenseRegistration. For me, the account login used the old address that my previous licenses were using. If that happens under your scenario then go through
the following steps
5. go back to your account settings in step 3 and click on Disconnect
6. Now go re-run the Show-WindowsDeveloperLicenseRegistration cmdlet, it should now prompt you for Name and password instead of just pre-filling in the name.
much appreciated,
mike