ol = ToFileName[{$InstallationDirectory, "SystemFiles", "FrontEnd",
"StyleSheets", "Utility"}, "Outline.nb"];
stylnbk = Import[ol];

insertToToolbar = {" | ", TooltipBox[ButtonBox["7", ButtonFunction :>
  (SelectionMove[ButtonNotebook[], After, Cell];
   NotebookWrite[ButtonNotebook[], Cell["XXXX", "Outline7"], All];
   SelectionMove[ButtonNotebook[], All, CellContents]),
 BaseStyle -> "ToolbarButton",
 Appearance -> None, ButtonFrame -> None,
 Evaluator -> Automatic,
 ImageSize -> Automatic, Method -> "Queued"],
"Insert outline level 7.", ActionDelay -> 0.35`]};

level7CellGroup = Cell[CellGroupData[{Cell[StyleData["Outline7"],
  CellMargins -> {{320, 10}, {7, 7}},
  ReturnCreatesNewCell -> True,
  StyleKeyMapping -> {"Backspace" -> "Outline6",
    KeyEvent["Tab", Modifiers -> {Shift}] -> "Outline6"},
  CellGroupingRules -> {"SectionGrouping", 110},
  DefaultNewCellStyle -> "Outline7",
  DefaultReturnCreatedCellStyle -> "Outline7",
  ParagraphIndent -> 0, CounterIncrements -> "Outline7",
  MenuSortingValue -> 1500,
  MenuCommandKey -> "7",
  FontFamily -> "Verdana",
  FontSize -> 10,
  CounterBoxOptions -> {CounterFunction :> (CharacterRange[
         "[GothicA]", "[GothicZ]"][[#1]] &)}],
 Cell[StyleData["Outline7", "Numbered"],
  CellDingbat -> StyleBox[RowBox[{CounterBox["Outline7"], "."}],
    FontFamily -> "Verdana", TextAlignment -> Right]],
 Cell[
  StyleData["Outline7", "PreviewNumbered",
   StyleDefinitions -> StyleData["Outline7", "Numbered"]]],
 Cell[StyleData["Outline7", "Bulleted"],
  CellDingbat -> "[FilledVerySmallSquare]"],
 Cell[
  StyleData["Outline7", "PreviewBulleted",
   StyleDefinitions -> StyleData["Outline7", "Bulleted"]]],
 Cell[StyleData["Outline7", "Presentation"],
  CellMargins -> {{350, 10}, {10, 10}}, FontSize -> 20]},
Closed]];

newStylSht = (stylnbk /.
    HoldPattern[DockedCells -> {Cell[BoxData[StyleBox[
        GridBox[{lst : {StyleBox["Outline Level: ", FontWeight -> "Bold"],
               PatternSequence[TooltipBox[__], " | "] ..,
               TooltipBox[__]}}, gbopts__], sbopts__]], cellopts__]}] :>
     DockedCells ->
      {Cell[BoxData[StyleBox[GridBox[{Join[lst, insertToToolbar]}, gbopts],
          sbopts]], cellopts]} /.
   HoldPattern[CounterAssignments -> cas : {{_, 0} ..}] :>
    CounterAssignments -> Insert[cas, {"Outline7", 0}, -1] /.
  HoldPattern[DefaultReturnCreatedCellStyle-> "Outline6"] :>
   Sequence[DefaultNewCellStyle -> "Outline7",
    DefaultReturnCreatedCellStyle-> "Outline6",
    CounterAssignments -> {{"Outline7", 0}}] /.
 HoldPattern[StyleKeyMapping -> skm:{"Backspace" -> "Outline5",
      KeyEvent["Tab", Modifiers -> {Shift}] -> "Outline5"}] :>
  StyleKeyMapping -> Insert[skm, "Tab" -> "Outline7", 1] /.
HoldPattern[Cell[CellGroupData[
    cgd:{Cell["Styles for Outline Documents", "Section"], ___}, opt___]]] :>
 Cell[CellGroupData[Insert[cgd, level7CellGroup, -1], opt]]);

flNm = ToFileName[{$InstallationDirectory, "SystemFiles", "FrontEnd",
   "StyleSheets", "Utility"},  "Outline7Levels.nb"];
NotebookSave[newStylSht, flNm]