So, if I have understood correctly, you need to select multiple levels from the same column. 'ComboBox()' forces you to make one selection, but you can try 'ListBox()' instead (use the SHIFT or CONTROL keys as you click the items in the list):
Names Default To Here( 1 );
// Make a table
n = 30;
MRB_List = {"Bin1", "Bin2", "Bin3", "Bin4", "Bin5", , "Bin6", , "Bin7", , "Bin8", , "Bin9", , "Bin10"};
MRBVals = {};
For( i = 1, i <= n, i++,
Insert Into( MRBVals, MRB_List[Random Integer( 1, N Items( MRB_List ) )] )
);
dt = New Table( "Bin Data", New Column( "BinClass_", Character, Nominal, Values( MRBVals ) ) );
// Make the UI
New Window( "MRB Filter", Outline Box( "Bin Selection/Exclusion" ), lb = List Box( MRB_List, cbScript ) );
cbScript = Expr(
myBins = lb << getselected;
dt << clearRowStates;
dt << selectWhere( Contains(myBins, :BinClass_ )) << Enable << Exclude << Hide;
);