If you're on a paid plan we've already reviewed your active listings and automatically removed the active content from them, so no you do not need to redo every listing. If you view your Auctiva Account Messages you should see a confirmation message where you can verify the results.
In the email I mentioned, "Once the new templates are released, you'll be able to access all of your customized listing templates from the "Manage" Custom Template page. To make them available in the new template system, you'll need to copy the template HTML from the "Manage" page and create a new custom listing template." This just means that if you have previously created a Customized Listing template and you want to continue using it, you'll need to save it as a new custom listing template to make it available in the new Template Selector.
I hope that helped clear up any confusion, but let me know if you have any other questions!