Hi
So can the group policy be changed later for domain users?
Thanks
Sure. Just remember that "domain users" is a very general term and they are subject to both the Default Domain Policy and to some extent the Default Domain Controller Policy. And then to any specific GPO (customized Admin Template, .adm, .admx) that may be unique to their particular OU container. As far as I know any GPO can be edited at any time.
If you are just learning just make sure you understand the cascading nature of how GPOs are applied (Local, Site, Domain and then OU last) and that they impact both domain users as well as domain computers.
And consider using tools like RSoP and GPResult (Google.... many tutorials, and videos) to help you better...