How do I change automatic logon via Script or Command Line?

One can change the registry via a .reg file.

For example, create an autologin.reg file containing :

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon]
"AutoAdminLogon"="1"
"DefaultUserName"="Administrator"
"DefaultPassword"="Pa$$w0rd"

Add DefaultDomainName if required, then just execute the file to get the values into the registry.

Or in a cmd script :

REG ADD "HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon" /v AutoAdminLogon /t REG_SZ /d 1 /f
REG ADD "HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon" /v DefaultDomainName /t REG_SZ /d domainname /f
REG ADD "HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon" /v DefaultUserName /t REG_SZ /d Administrator /f
REG ADD "HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon" /v DefaultPassword /t REG_SZ /d Pa$$w0rd /f

_{(Warning: I didn't test the above.)}

Can't you just use sysprep /oobe? It will finalize your install and show the welcome screen on reboot.

Read what sysprep is and how sysprep works for more information.

Sysinternal's Autologon should be able to auto logon only once. That was a function when I've used it a while ago but I'm not seeing any details on whether it does that now.