Hello.
I am not sure what examples do you refer to, but you can do this like this:
//Get PageInfo
System.Guid g = new Guid("68846B3F-1C79-4C9D-8BDB-B4BC0414D2FE");
PageInfo pi = PageInfoProvider.GetPageInfo(g);
//Set value
pi.EditableRegions["toptext"] = "Radek";
TreeProvider tr = new TreeProvider();
TreeNode tn = tr.SelectSingleNode(CMSContext.CurrentDocument.DocumentID);
// Update the content XML
tn.SetValue("DocumentContent", pi.DocumentContent);
// Update the document
DocumentHelper.UpdateDocument(tn, tr);
Best Regards,
Radek Macalik