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

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

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.

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?

The Page version link plugin no longer exists for newer confluence versions. But I've found the Scroll Versions Plugin which supports the link to a specific version of a page.

Additionally it has many more features like editing multiple versions of a page in a single space and publishing all/selected pages of a specific versions when you have finished it.