In Confluence, how do I create a permanant link to a specific version of a page when that page is the current version?

AFAIK, you can't without a custom plugin to handle links with versions. Confluence will always use the pageId of the original page as the latest version and insert a new pageId for historical versions as they are created. For example, your current page has pageId 21364790 and version 2; editing the page creates a new pageId 21364791 as a copy of the previous version, and updates 21364790 with your changes. This means that there is no way to predict what the pageId of a historical version will be when it is currently the latest version.

I see two solutions. The more elegant solution is to make a plugin providing a copy of the XWork viewpage action, and giving it a version parameter. You could then access the correct version using a URL like http://wiki/pages/myviewpage.action?pageId=21364790&version=2. The ugly hack solution is to double-up your edits, so you can be sure of what the correct historical pageId will be.

You can do it manually by specifying the version of the page in URL - http://wiki/pages/viewpage.action?pageId=21364790&pageVersion=1

But even better to have something similar to https://marketplace.atlassian.com/plugins/com.k15t.scroll.scroll-versions

Page version link plugin

This plugin adds to a header of every page the link, referring to the displayed version of the page regardless of any future content updates.

Is it what you need?