Mobile navigation sub menus

Replying to myself here, just in case it's useful for someone else in the future, this is not elegant and I'm sure there are much better ways, but I am not a developer and it worked for me:

beans_modify_action_callback( 'beans_modify_menu_args', 'your_theme_modify_menu_args' );

function your_theme_modify_menu_args( $args ) { 
    // contents of beans_modify_menu_args with any modifications for your theme
    // (see https://github.com/Getbeans/Beans/blob/release/1.5.0/lib/render/menu.php)
    // in my case, I deleted the line specifying data-uk-nav for offcanvas menus
}