You can use following workarounds:

1)The menu items are components and you can edit any menu item directly in your code. For example:
this.radMenuItem10.Click+=menuItemClickMethod;

Also you can selected and edit them in these ways:

2) Selected a particular menu item via Visual Studio's Document Outline window (ctrl+W, U). Then you will be able to selected the desired item from the hierarchy. After that item will be selected in the property grid and you can add/remove events and edit its properties.

3) You can select a specific menu item directly via Visual Studio's Property Grid's Component combobox (on the top of the property grid)