Problem changing Model Reference from GUI

I launch a model from a GUI, and depending on what options are selected in the GUI, some model references should change. Currently, the model reference is set to have the following two variants:

CoolSys1 name 1

CoolSys2 name 2

I then add the following in a button push callback in the gui

CoolSys1 = Simulink.Variant('cs_Version==0');

CoolSys2 = Simulink.Variant('cs_Version==1');

cs_Version = get(handles.ShutterEnabled,'Value'));

I have also tried to add the Simulink.Variants to the handles of the GUI, to the model workspace and to the base workspace, but wherever I place them the model won't run and I get the following error:

Caused by:
    Error using run_batchGUI (line 126)
    The variant 'CoolSys1' of the variant block '.../Referenced Model (CoolSys)' must be the name of a Simulink.Variant object in the base workspace.

      Error using run_batchGUI (line 126)
      The variant 'CoolSys2' of the variant block '.../Referenced Model (CoolSys)' must be the name of a Simulink.Variant object in the base workspace.

Error while evaluating uicontrol Callback

I repeat, I get that error even when I DO have CoolSys1 and CoolSys2 in the model's and the base workpaces.

What can I do about this?