Filter the Broadsheet slider properties

broadsheet-slider-params.php

<?php
/**
 * Plugin Name: Change Broadsheet slide quantity
 * Plugin URI: https://prothemedesign.com
 * Description: Change number of posts that appear in the Broadsheet slider.
 * Author: Ben Gillbanks
 * Version: 1.0
 * Author URI: https://prothemedesign.com
 * Text Domain: broadsheet
 */

function broadsheet_slider( $params ) {

	$params['posts_per_page'] = 4;
	return $params;

}

add_filter( 'broadsheet_slider', 'broadsheet_slider' );