Eigene Dateiendung die wie .bat behandelt werden soll

function InstallExt(Extension, ExtDescription, FileDescription,
                    OpenWith, ParamString: String; IconIndex: Integer): Boolean;
var
  Reg: TRegistry;
begin
  Reg := TRegistry.Create;
  try
    try
      with Reg do
      begin
        RootKey := HKEY_CLASSES_ROOT;
        OpenKey(Extension, True);
        WriteString('', ExtDescription);  
        CloseKey;
        OpenKey('\' + ExtDescription, True);  
        WriteString('', FileDescription);  
        CloseKey;
        OpenKey('DefaultIcon', True);  
        WriteString('', OpenWith + ','+IntToStr(IconIndex));  
        CloseKey;
        OpenKey('\' + ExtDescription + '\Shell\Open\Command', True);  
        WriteString('', '"' + OpenWith + '" "' + ParamString + '"');  
        CloseKey;
      end;
      Result := True;
    except
      Result := False;
    end;
  finally
    Reg.Free;
  end;
end;
Begin
InstallExt('.test', 'test-Datei', 'test', 'C:\Windows\System32\cmd.exe', '%1',0);  
end.