The Menu Editor lets you customize 3ds Max menus and quad menus.
The Menu Editor displays the currently loaded menu and quad menu configurations, and lets you customize them by adding or removing menu items. Customized configurations are stored in .mnx files (for menus) and .qmnx files (for quad menus). These files can be copied and used in later versions of 3ds Max to preserve your customizations.
On this dialog you can:
To add a new menu item:
To delete a menu or menu item:
To find the menu associated with an action:
To edit the script associated with a menu item:
Right-click the menu item or action you want to edit.
Select Edit Macro Script.
The Script Editor opens displaying the script that defines the item.

Menus Tab
Lets you choose the menu configuration to edit.
Action items are organized into groups related to their feature area. This drop-down lets you specify which group of action items to look at.
Lets you filter the list of action items by keyword.
Lists action items by name, and including their group and category, where assigned. From this list you can right-click items to see where they are used in the menu tree, and to edit their underlying macroscripts. You can also drag items from this list into the menu structure on the right to create a new menu item.
Lets you select a menu to edit.
Provides a tree view of sub-menus and menu items in the menu selected in the Edit Menu list.
Quads Tab
Lets you choose the quad menu configuration to edit.
Action items are organized into groups related to their feature area. This drop-down lets you specify which group of action items to look at.
Lets you filter the list of action items by keyword.
Lists action items by name, and including their group and category, where assigned. From this list you can right-click items to see where they are used in the menu tree, and to edit their underlying macroscripts. You can also drag items from this list into the menu structure on the right to create a new quad menu item.
Lets you edit the selected quad menu. In this list you can add new quad menu items, as well as rename, re-order, and delete existing items. You can also create sub-menus and separators. You can right-click an existing item, and view its corresponding action in the action item list.
The Menu Editor includes a Developer Mode, which you access by selecting the settings icon:

This mode is intended for developers who want to create menu customization files for their plug-ins. In Developer Mode, you can access additional functionality useful for developing plug-ins that expose their own menus or modify / add to existing ones.
When you switch to Developer Mode, only the base menu configuration and either the selected preset or an empty preset is loaded; plug-in and user defined menus are not loaded. This simplifies the menu structure and provides a clean configuration for a developer to work with. As a developer, you can add menu items to existing menus (for example, the main menu bar), or create new top-level menus for use as a menu bar in your dialog or right-click context menu.
Developer Mode lets you create, rename, and delete top-level menus. Top-level menus can then be used as a menu bar or right-click context menu in a plug-in.
Customizations are saved as a .mnx or .qmnx transformation file ("Save as..."). The "Save as Base Configuration" option is for internal use only.
For Quad menus, in Developer Mode you get an additional Quad Menu Context selection, to display only the quad menus in that context. This lets you add/rename/delete quad menus for a specific context, and more importantly, create a new quad menu context for use in your own plug-in. In non-Developer mode, Quad menus are listed for all contexts.
Developer mode also provides access to the localization workflow. This is a resource ID based workflow, very similar to the existing process for localizing MAXScript string resources (See the "Resource String Replacement" topic in the MAXScript help for more information).
To localize a configuration, select "Create localization file", and select a target .mnx or .qmnx file. This creates a skeleton resource file for the configuration file, which contains the resource ID and display text for each item in the menu/quad. This file is then copied and translated for each target language. Once translated, the .res file is placed in the target language sub-directory for the plug-in (for example, for French, in a directory called fr-FR under the directory containing the .mnx/.qmnx file).