好的，这可以使用JavaScript（jQuery-lib）实现。代码-

// load jquery on login screen if not loaded already
add_action( \'login_enqueue_scripts\', \'wpse_login_head\' );
function wpse_login_head(){
    wp_enqueue_script(\'jquery\');
}

add_action( \'register_form\', \'wpse_register_form\' );
function wpse_register_form(){ ?>

    <!-- we have used an unique id for the description tag -->
    <span id="user_login_description" style=" display:none;" class="description"><?php _e("Description text"); ?></span>

    <!-- the following line of code move the description after the username input -->
    <script type="text/javascript">jQuery(\'#user_login_description\').appendTo(\'#registerform p:nth-child(1) label\').show();</script>
   <?php
}