Sub Mein_Button1()
   Dim cmbStandard As CommandBar
   Set cmbStandard = Application.ActiveExplorer.CommandBars("Standard")
      With cmbStandard.Controls.Add
         .BeginGroup = True
         .Caption = "Mein Button"
         .Style = msoButtonCaption
         .OnAction = "Test"
      End With
End Sub

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Sub Test()
   MsgBox "Ich bin der CommandButton-Test"
End Sub