Customize SearchWP stopwords per Engine

searchwp-customizations.php

<?php

/**
 * Customize SearchWP stopwords per Engine.
 */

// Optional: remove all Stopwords so you can add only unique Stopwords per Engine.
add_filter( 'searchwp\stopwords', '__return_empty_array' );

// Add unique stopword(s) for a single SearchWP Engine.
add_filter( 'searchwp\query\search_string', function( $search_string, $query ) {
  // Remove "apple" and "orange" for my_engine searches.
  if ( 'my_engine' === $query->get_engine() ) {
    $search_string = str_replace( [ 'apple', 'orange' ], '', $search_string );
  }

  return $search_string;
}, 20, 2 );