Option Explicit
Private Sub Document_ContentControlOnExit(ByVal ContentControl As ContentControl, Cancel As Boolean)
Dim oCC As ContentControl
    Select Case ContentControl.Title
        Case "DropDownBoxTitle"
            Set oCC = ActiveDocument.SelectContentControlsByTitle("Code Text").Item(1)
            If ContentControl.ShowingPlaceholderText = False Then
                Select Case ContentControl.Range.Text
                    Case "1": oCC.Range.Text = "Text for item 1"
                    Case "2": oCC.Range.Text = "Text for item 2"
                        'etc
                End Select
            End If
        Case Else
    End Select
    Set oCC = Nothing
End Sub