SunAndShadowSettings sunSettings = commandData.Application.ActiveUIDocument.ActiveView.SunAndShadowSettings;
using (Transaction tr = new Transaction(doc, "SetSunAndShadowChanges"))
{
tr.Start();
sunSettings.SunAndShadowType = SunAndShadowType.MultiDayStudy;
view.get_Parameter(BuiltInParameter.VIEW_GRAPH_SUN_PATH).Set(1);
tr.Commit();
}