Loads a set of menus from a menu file (see FILE_FORMAT for details of the format). The number of menus which may be active at any one time is limited to five, however, a button may be set to load a further set of menus and activate them. So, using this technique, the number of menus which may be interlinked becomes unlimited.
Standard Asterix menus are kept in the $AST_DAT_MENU directory. Take a copy of the img.mnu file and edit it to your tastes.