functions.php

<?php

function my_searchwp_engine_customizations( $settings, $query ) {
	// print_r( $settings );    // uncomment this line to see the settings structure
	// print_r( $query );       // uncomment this line to see the query structure

	// Check for Title-only search
	if ( empty( $_REQUEST['searchwp_limit_to_title'] ) ) {
		return $settings;
	}

	// Set all weights to zero except Title
	foreach ( $settings as $post_type => $post_type_settings ) {

		// If the post type isn't enabled, skip to the next
		if ( empty( $post_type_settings['enabled'] ) ) {
			continue;
		}

		// Set all weights to zero excerpt Titles
		foreach ( $post_type_settings['weights'] as $content_type => $weight ) {
			switch ( $content_type ) {
				case 'title':
					continue;
					break;

				case 'tax':
					// Taxonomies have a different structure
					foreach ( $weight as $taxonomy => $taxonomy_weight ) {
						$settings[ $post_type ]['weights'][ $content_type ][ $taxonomy ] = 0;
					}
					break;

				case 'cf':
					// Custom Fields have a different structure
					foreach ( $weight as $custom_field_uid => $custom_field_weight_pair ) {
						$settings[ $post_type ]['weights'][ $content_type ][ $custom_field_uid ]['weight'] = 0;
					}
					break;

				default:
					$settings[ $post_type ]['weights'][ $content_type ] = 0;
			}
		}
	}
	
	// Self unhook
	remove_filter( 'searchwp_engine_settings_default', 'my_searchwp_engine_customizations', 10, 2 );

	return $settings;
}

add_filter( 'searchwp_engine_settings_default', 'my_searchwp_engine_customizations', 10, 2 );