Private Sub Workbook_Open()
    Dim ws As Worksheet
    
    On Error Resume Next
    
    For Each ws In ThisWorkbook.Worksheets
        ws.Unprotect Password:="123"
        ws.EnableSelection = xlUnlockedCells
        ws.Protect Password:="123", _
          DrawingObjects:=True, _
          Contents:=True, _
          Scenarios:=True
    Next ws
End Sub

Private Sub Worksheet_BeforeDoubleClick( _
  ByVal Target As Range, _
  Cancel As Boolean)
    If Target.Address = "$A$1" Then
        MsgBox "Нельзя изменять!"
        Cancel = True
    End If
End Sub

Private Sub Worksheet_Change( _
  ByVal Target As Range)
    If Target.Address = "$A$1" Then
        Application.EnableEvents = False
        Target.Value = ""
        MsgBox "Нельзя изменять!"
        Application.EnableEvents = True
    End If
End Sub