VBA is not my particular strength, but here we go:
I would like to trigger a macro once a group of columns is hidden or shown. How can I archive this?
The results of my previous research
The only good hint about this I could find is this discussion at MSDN. Here, a solution is using the following way is drafted:
From the root dir of the xlsx file create a file customUI\customUI.xml with the content 
<customUI  xmlns="http://schemas.microsoft.com/office/2006/01/customui" >
    <commands >
        <command 
            idMso="ColumnsHide"
            onAction="ColumnHide_onAction"/>
        <command 
            idMso="ColumnsUnhide"
            onAction="ColumnUnhide_onAction"/>
    </commands >
</customUI >
and add
<Relationship Id="edTAB" Type="http://schemas.microsoft.com/office/2006/relationships/ui/extensibility" Target="customUI/customUI.xml" />
to the _rels\_rels.xml. (All this probably is much easier using Visual Studio, but I have no access to such sophisticated tools in the microsoft world...) Now, the macro can be used the following way:
Public Sub ColumnHide_onAction(control As IRibbonControl, ByRef cancelDefault)
'
' Code for onAction callback. Ribbon control command
'
    MsgBox "Ribbon Column Hide"
    cancelDefault = False
End Sub
Public Sub ColumnUnhide_onAction(control As IRibbonControl, ByRef cancelDefault)
'
' Code for onAction callback. Ribbon control command
'
    MsgBox "Ribbon Column Unhide"
    cancelDefault = False
End Sub
This approach perfectly catches hiding and unhiding of columns, but not hiding and unhiding of groups. So, close, but not quite there.
Downloading the possible idMso values from here, I got notice of the GroupViewShowHide control. Using this the same way as ColumnsHide or ColumnsUnhide does not archive the desired result, though.
Any ideas?
 
     
    