Exporting selected pages to another WP website

I couldn’t find any useful hooks in export_wp(), maybe you could reverse the problem by restricting the import instead?

You might check out the filter wp_import_posts, you can find it in /wp-content/plugins/wordpress-importer/wordpress-importer.php:

/**
         * Create new posts based on import information
         *
         * Posts marked as having a parent which doesn't exist will become top level items.
         * Doesn't create a new post if: the post type doesn't exist, the given post ID
         * is already noted as imported or a post with the same title and date already exists.
         * Note that new/updated terms, comments and meta are imported for the last of the above.
         */
        function process_posts() {
                $this->posts = apply_filters( 'wp_import_posts', $this->posts );

                foreach ( $this->posts as $post ) {
                        $post = apply_filters( 'wp_import_post_data_raw', $post );

// cut