Stop pinned tabs changing in Chrome
I do not believe there is an extension that will keep your tab from changing the URL, pinned or otherwise.
I created an extension that tries to keep the tab on the same page. When you click on any link it will open that link in a new tab rather than replacing the current tab. If you type a different URL in the location bar, it won't open a new tab. Unfortunately, I couldn't find a way to prevent that through the Chrome extension APIs.
https://github.com/pmcelhaney/static-pinned-tab-chrome-extension