FacetWP, plus Relevansii, via a keyword facet

Ok, this subject sort of came up a couple of times, but not exactly addressing my situation: I set up FacetWP with Relevanssi and FacetWP has a keyword facet that redirects to a custom page instead of search.php for search results. It works fantastically and allows developers to design a search results page that looks like their theme. I love Highlight Search Terms but as others pointed out, it doesn’t work when searches bypass search.php page. Somebody asked 9 months ago “Doesn’t work with Search & Filter plugin?” and the solution may be applicable in my situation. However, I can’t figure out where the code you offered should go. Custom Hooks? Directly in hlst.php? Replacing something or added in line 154? And is this the code?

elseif ( isset($_GET[‘_sf_s’]) AND $search = $_GET[‘_sf_s’] )
self::$search_terms = self::split_search_terms( $search );

Thanks!