Hi Felix,
You can not just ''set'' cell specific properties (other than the CellValue) in a GridGroupingControl. You can set column wide styles using grid.tableDescriptor.Column[x].Appearance property, you can set conditional row formats by adding ConditionalFormats. See this thread.
http://www.syncfusion.com/Support/Forums/message.aspx?MessageID=26929that shows you "How to set cell-specific property in a grid?".
In version 5.1, we ship a sample that shows how style settings can be applied dynamically. If you want to provide formatting at run time, the QueryCellStyleInfo event handler is the right place to do that. It provides the GridStyleInfo object for a given cell on demand. This is the event that gets fired, every time a request is made, to access the style information for a cell. It is also used to conditionally change the style for a given cell. Inside this handler, you can apply style settings for a given celltype by using the GridTableCellStyleInfoEventArgs.TableCellIdentity.TableCellType property.Below is a link to this sample.
\Syncfusion\EssentialStudio\5.1.1.0\Windows\Grid.Grouping.Windows\Samples\2.0\Appearance\DynamicFormatting\csBest regards,
Haneef