Автор: http://www.swissdelphicenter.ch

uses
  Registry;

procedure AddFileMenue(FilePrefix, Menue, Command: string);
var
  reg: TRegistry;
  typ: string;
begin
  reg := TRegistry.Create;
  with reg do
  begin
    RootKey := HKEY_CLASSES_ROOT;
    OpenKey('.' + FilePrefix, True);
    typ := ReadString('');
    if typ = '' then
    begin
      typ := Fileprefix + 'file';
      WriteString('', typ);
    end;
    CloseKey;
    OpenKey(typ + '\shell\' + Menue + '\command', True);
    WriteString('', command + ' "%1"');
    CloseKey;
    Free;
  end;
end;

procedure DeleteFileMenue(Fileprefix, Menue: string);
var
  reg: TRegistry;
  typ: string;
begin
  reg := TRegistry.Create;
  with reg do
  begin
    RootKey := HKEY_CLASSES_ROOT;
    OpenKey('.' + Fileprefix, True);
    typ := ReadString('');
    CloseKey;
    OpenKey(typ + '\shell', True);
    DeleteKey(Menue);
    CloseKey;
    Free;
  end;
end;

{ Example / Beispiel:}

procedure TForm1.Button1Click(Sender: TObject);
begin
  { Register the Menuepoint: }

  AddFileMenue('rtf', 'Edit with Notepad', 'C:\Windows\system\notepad.exe');

  {
    If you now click with the right mousebutton on a *.rtf-file then
    you can see a Menuepoint: "Edit with Notepad".
    When Click on that point Notepad opens the file.

    Wenn man nun mit der rechten Maustaste im Explorer auf eine *.rtf-Datei Clickt,
    dann erscheint dort der Menuepunkt "Edit with Notepad".
    Beim Clicken darauf, цffnet Notepad diese Datei.
  }
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  {
   Unregister the Menuepoint / Undo your changes in the Registry:
   Lцscht den Menuepunkt wieder aus der Registry:
  }

  DeleteFileMenue('rtf', 'Edit with Notepad');
end;