这将获取所有带有$old\\u tax的帖子，将条款从$old\\u tax复制到$new\\u tax，然后为这些帖子设置$new\\u tax条款。

<?php
    function convert_tax($old_tax, $new_tax) {
        $pages = get_posts(array(
            \'post_type\' => \'post\',
            \'posts_per_page\' => -1,
            \'tax_query\' => array(
                array(
                    \'taxonomy\' => $old_tax,
                    \'operator\' => \'EXISTS\'
                )
            )
        ));

        foreach($pages as $post) {
            $terms = get_the_terms( $post->ID, $old_tax );
            $term = array();

            foreach( $terms as $t ) {
                if( get_term_by( \'name\', $t->name, $new_tax ) == false ) {
                    wp_insert_term( $t->name, $new_tax, $args = array() );
                    wp_set_post_terms($post->ID, array(intval($t->ID)), $new_tax ); 
                }
            }
        }
    }

    convert_tax(\'policy_area\', \'topic\')

?>

只要文章分类法中的slug与默认类别中的slug完全对应，您就应该能够为每篇文章执行类似的操作：

        $article_cats = wp_get_object_terms( $article_id, \'article-category\' );
        $new_cats = array();
        foreach( $article_cats AS $t ) {
            $new_cats[] = $t->slug;
        }
        wp_set_object_terms( $post_id, $new_cats, \'categories\' );