Customize the SearchWP engine used in EDD Integration

functions.php

<?php

function searchwp_edd_engine( $engine, $query, $atts ) {
  return 'default'; // the name of the engine you want to use for the [downloads] Shortcode
}

add_filter( 'searchwp_edd_engine', 'my_searchwp_edd_engine', 10, 3 );