potatohark

Not sure if this is the best solution, but I included the following in my footer:

<script>
		function get_var(var_name){
			var query = window.location.search.substring(1);
			var vars = query.split("&");
			for (var i=0;i<vars.length;i++) {
				var pair = vars[i].split("=");
				if(pair[0] == var_name){return pair[1];}
			}
			return(false);
		}

		var get_variable = get_var("pwb-brand");
		if (get_variable !== '') {

			document.getElementsByClassName("products clearfix products-1")[0].setAttribute("class", "products clearfix products-3");
		}
	</script>