If you have a menu item of type ITEM_TYPE_LISTBOX that lists maps/players/mods using the feeder property (like in the server creation menu ui_mp/createserver.menu), I see no direct way to set the current selection as the input is handled via the game internal menu system. The player has to use either the mouse as input, or some specific keys (KEY_PGDN, KEY_PGUP, KEY_DOWN, KEY_UP and keypad equivalents). Does that help?