Combo Boxes Passing Selections to Other Dashboards

 it may help to use the same bound parameter across multiple comboboxes that need to display the same default choice, or just use the same combobox with its bound parameter.  You can also pass the value of the combobox bound parameter to the Dashboard Extender rule by assigning it to an argument {DBExtenderRule}{ComboboxFunction}{combo1Val=|!pm_combo1val!|}.  Then assign it to another parameter in the rule:

Dim taskResult As XFSelectionChangedTaskResult = New XFSelectionChangedTaskResult() With {
    .IsOK = True,
    .ShowMessageBox = False,
    .Message = "",
    .ChangeSelectionChangedUIActionInDashboard = False,
    .ChangeSelectionChangedNavigationInDashboard = False,
    .ChangeCustomSubstVarsInDashboard = true,
    .ChangeCustomSubstVarsInLaunchedDashboard = False
}

taskResult.ModifiedCustomSubvars("combo2Val) = combo1Val

Return taskResult