Can a Combobox set its value dynamically on a dashboard load/refresh?

Here you go. This example is using literal parameters to set the combo boxes but you could pass through parameters on the extender call to do it instead of the literal parameters. Also at the top of this call it will only run this rule on the intial load of the dashboard which I believe is what you would want to do.

Case Is = DashboardExtenderFunctionType.LoadDashboard
                        If (args.FunctionName.XFEqualsIgnoreCase("OnLoadWaterFallDashboard")) Then 
                            If args.LoadDashboardTaskInfo.Reason = LoadDashboardReasonType.Initialize And args.LoadDashboardTaskInfo.Action = LoadDashboardActionType.BeforeFirstGetParameters Then' Or LoadDashboardReasonType.ComponentSelectionChanged Then '                                 'Initialize Message 
                                Dim loadDashboardTaskResult As New XFLoadDashboardTaskResult() 
                                loadDashboardTaskResult.ChangeCustomSubstVarsInDashboard = True 
                                Dim Comp2Scn As String = BRApi.Dashboards.Parameters.GetLiteralParameterValue(si, False, "Param_Water_LiteralSelectComp2Scn")
                                Dim Comp2Time As String = BRApi.Dashboards.Parameters.GetLiteralParameterValue(si, False, "Param_Water_LiteralSelectComp2Time")
                                Dim Comp1Scn As String = BRApi.Dashboards.Parameters.GetLiteralParameterValue(si, False, "Param_Water_LiteralSelectComp1Scn")
                                Dim Comp1Time As String = BRApi.Dashboards.Parameters.GetLiteralParameterValue(si, False, "Param_Water_LiteralSelectComp1Time")
                                Dim CurScn As String = BRApi.Dashboards.Parameters.GetLiteralParameterValue(si, False, "Param_Water_LiteralSelectCurScn")
                                Dim CurTime As String = BRApi.Dashboards.Parameters.GetLiteralParameterValue(si, False, "Param_Water_LiteralSelectCurTime")
                            'Brapi.ErrorLog.LogMessage(si, Comp2Scn & Comp2Time &Comp1Scn &Comp1Time &CurScn &CurTime )
                                loadDashboardTaskResult.ModifiedCustomSubstVars.Add("Param_GPS_SelCompFCast", Comp1Scn) 
                                loadDashboardTaskResult.ModifiedCustomSubstVars.Add("Param_GPS_SelCompFcstTimeMth", Comp1Time) 
                                loadDashboardTaskResult.ModifiedCustomSubstVars.Add("Param_GPS_SelComp2FCast", Comp2Scn) 
                                loadDashboardTaskResult.ModifiedCustomSubstVars.Add("Param_GPS_SelComp2FcstTimeMth", Comp2Time) 
                                loadDashboardTaskResult.ModifiedCustomSubstVars.Add("Param_SelectCurFcst", CurScn) 
                                loadDashboardTaskResult.ModifiedCustomSubstVars.Add("Param_SelectCurFcstTimeMth", CurTime)                                 
                                    Return loadDashboardTaskResult 
                            End If 
                        End If

THanks,