For the sake of simplicity, I will create two dummy files for examples.
What I'm trying to do is create a form that modifies small sections of html, so users can customize what is displayed with a very basic interface.

Form:

Site: [SiteID]

To process a simple, same page, text description where the form data changes ONE value in the html markup.

For example:

<html>
<head></head>
<body>
<div class="container">
<p class="small">[SiteID]</p>
</div>
</body>
</html>

Simply output to same page in a text box with that info in text format.

Any easy suggestions for a JS solution to this?