Here's how to add pubDate and guid fields to your RSS output from JSON input. -- http://pipes.tumblr.com/post/32331202

You can use the contents of fields in your regex replacements; just use the ${fieldname} pattern. This works even if you use it inside a String Builder. In this demo, notice how the publication date becomes part of the title. -- http://pipes.tumblr.com/post/32153703