Override the Pro Theme header assignment for specific pages and conditions

override-header-assignment-5.php

add_filter('cs_match_header_assignment', 'custom_search_header');
function custom_search_header($match) {
	$user = wp_get_current_user();
	if (is_search()) {
		$match = 1234; // the post ID for your header
	}
	elseif (is_404()) {
		$match = 4567; // the post ID for your header
	}
	return $match;
}