Use a supplemental search engine name to reset the limit on number of accepted search terms per search query

gistfile1.php

<?php

function my_searchwp_max_search_terms_my_search_engine( $maxTerms ) {
  // limit to 8 search terms for My Supplemental Search Engine ONLY
  return 8;
}
add_filter( 'searchwp_max_search_terms_my_search_engine', 'my_searchwp_max_search_terms_my_search_engine', 10, 2 );