I have a domain controller running Server 2003 and the goal is to create a GPO for the domain without using a GUI program (no gpedit, gpmsc, etc.). How can I achieve this goal by using cmd only? (powershell doesn't exist on the server either)
Yes, it is possible, using
New-GPO command on powershell.
On a modern Windows 10 client with
rsat tools installed and also adding Module:
grouppolicy in powershell. You can execute commands to administer and modify a domain from a client, that's what
rsat is for. You don't need to do this tasks from a server. Yet I can't tell if this modern powershell commands can administer a Windows server 2003 domain. If you were on newer version, it surely could be done. You could give it a try.
Have a look at this MS link, there are all the commands to manipulate GPOs from powershell.