Attention: This notebook contains initialization cells!

FrontEndExecute[ {FrontEnd`SelectionMove[SelectedNotebook[ ], All, 
          EvaluationCell], 
        FrontEnd`SelectionMove[SelectedNotebook[ ], Previous, 
          Cell]}]
SetOptions[NotebookSelection[SelectedNotebook[]], 
      CellOpen -> False]

This one does not work yet!
FrontEndExecute[FrontEndTokenExecute["Cell Open"]]

Note: Move the selection to the end of the page when done!