尝试将此插件放入wp-content/plugins 文件夹，然后将其激活：

<?php

/*
Plugin Name: WPSE53245 - Set Tweet category posts as Aside
Plugin URI: http://http://wordpress.stackexchange.com/questions/53235
Description: Set Tweet category posts as Aside
Version: 0.1
Author: Ashfame
Author URI: http://wordpress.stackexchange.com/users/1521/ashfame
*/

    add_action( \'save_post\', \'wpse53235_set_post_format_aside\' );

    function wpse53235_set_post_format_aside( $postID ) {
        if ( has_post_format( \'aside\', $postID ) || !has_term( \'tweet\', \'category\', $postID ) )
            return;
        set_post_format( $postID, \'aside\' );
    }