Editing a Group Policy Object (GPO)

I need to use PowerShell to edit a Group Policy object (GPO).
The setting I need to edit is:

User confnguration
 Policies
  Windows settings
   Internet Explorer Maintenance
    Security
     Security Zones and Content Ratings

and i need to add a site to the Trusted sites list.
I found interesting samples of PowerShell scripts to edit the list of trusted sites by editing the Registry, but I need to edit the GPO instead.
Is it possible?
Is there any example I can start from?
Regards and Season's greetings
marius