ajayver

This plugin gives you the ability to change the appearance of your RSS feed. You can easily add images from custom fields, read more link, category list, tag list and any custom code before or after the feed items. Also, the plugin allows you to delay feed publication for several minutes. It is helpful, when you made some mistake and you will have time to fix it before the post went to RSS and all other services like facebook or twitter.

RSS Manager

This plugin gives you the ability to change the appearance of your RSS feed.

Xiangxu

Clickit Readmore allows you to wrap any content inside a [read-more] shortcode to hide it until the user clicks a button. 
It provides a backend settings page where you can fully customize the “Read More” button, including:
<ul>
<li>Button background color </li>
<li>Hover background color </li>
<li>Button text color </li>
<li>Hover text color </li>
<li>Font size </li>
<li>Padding </li>
</ul>
This plugin is perfect for long posts, FAQs, product descriptions, or any content you want to initially hide for a cleaner layout.

Clickit Readmore

A lightweight and easy-to-use plugin that adds a customizable "Read More" toggle shortcode with a settings page to control button styles.

RSS Manager vs Clickit Readmore