后期保存后（使用save_post hook) 您可以检查保存的帖子是否有您的“唯一”类别，如果有，请从其他帖子中删除该类别，保留您刚刚保存的帖子。

add_action( \'save_post\', \'set_post_unique_category\', 10,3 );

function set_post_unique_category( $post_id, $savedPost, $update ) {

    // Only set for post_type = post
    if ( \'post\' !== $savedPost->post_type ) {
        return;
    }

    // Check if post has your desired category
    if ( ! has_category(\'best-post\', $savedPost) ){ //use your category slug
        return;
    }

    // Get the best-post category term by its slug
    $term = get_term_by( \'slug\', \'best-post\', \'category\' );

    //Now let\'s find the other posts with your category
    $args = array( \'category\' => $term->term_id, \'post_type\' =>  \'post\' );  //set the arguments for the query
    $postsList = get_posts( $args );  

    foreach ($postsList as $post) { //Remove the category from the found posts
         if ($post->ID == $post_id ) //but skip the just saved post
              continue;

         wp_remove_object_terms( $post->ID, \'best-post\', \'category\' );
    }



}

我没有测试它，因此您可能会遇到语法错误或错误的属性名称，但逻辑应该很好，至少可以让您了解应该做什么。好的谷歌搜索加上wordpress codex漫步永远是你的朋友；）