gistfile1.cs

            var content = ApplicationContext.Services.ContentService.GetById(1051);
            var data = new GridRowCollection();
            string[] nodeIds = {"1051", "1052"};
            foreach (string companyNodeId in nodeIds)
            {                
                Node node = uQuery.GetNode(companyNodeId);
                var row = new GridRow();
                var companyCell = new GridCell() { DataType = 1034, Alias = "nodePicker", Name = node.Name, Value = node.Id.ToString()};
                var permissionCell = new GridCell { DataType = -42, Alias = "permission", Name = "Permission", Value = "7" };
                row.Add(companyCell);
                row.Add(permissionCell);
                data.Add(row);
            }

            content.SetValue("datatypeGrid", data.ToString());
            ApplicationContext.Services.ContentService.SaveAndPublish(content);
            
            // Umbraco XML:
            <datatypeGrid>
                    <items>
                      <item id="0" sortOrder="1">
                        <nodePicker nodeName="Installing modules" nodeType="1034">1051</nodePicker>
                        <permission nodeName="Permission" nodeType="-42">7</permission>
                      </item>
                      <item id="0" sortOrder="2">
                        <nodePicker nodeName="Go further" nodeType="1034">1052</nodePicker>
                        <permission nodeName="Permission" nodeType="-42">7</permission>
                      </item>
                    </items>
                  </datatypeGrid>