How may one add some functionality to publicly available source code for which the license forbids modification?
<p>Is there a way way to add some new functionality to publicly available source code (rewrite completely?) and publish the modified version if the license goes as "You may redistribute the source code of this program subject to the condition that you do not first modify it in any way"?</p>

<h2><strong>No</strong></h2>

<p>You may not redistribute a copyrighted work under a license except in compliance with the terms of that license. If the license does not permit you to distribute modified versions, than doing so would be a copyright infringement. I cannot see how this would fall under fair use or fair dealing. So assuming that the copyright is valid, one would need to obtain permission from the copyright holder. A modified version of source code is a derivative work, and the right to prepare and distribute derivative works is one of the rights that together make up copyright. </p>

<p>If someone were to distribute, in violation of the license, and without such separate permission, a modified version, the copyright holder could sue, and quite possibly be awarded damages, perhaps sizable damages.</p>

<p>However, if one were to merely take the general purpose and design of the previous application, and rewrite it totally, not copying or modifying the original source code, tht would be a new and different work with its own copyright.  Copyright does not protect ideas or concepts. It protects the <strong>expression</strong> of ideas. Writing a novel about a quest to destroy evil does not infringe the copyright on <em>The Lord of the Rings</em> And writing a new spreadsheet program does not infringe the copyright on Microsoft Excel. But directly copying the source code would infringe.</p>

software licensing