Function XPLMSetMenuItemName 

pub unsafe extern "C" fn XPLMSetMenuItemName(
    inMenu: XPLMMenuID,
    inIndex: c_int,
    inItemName: *const c_char,
    inDeprecatedAndIgnored: c_int,
)

XPLMSetMenuItemName

This routine changes the name of an existing menu item. Pass in the menu ID and the index of the menu item.