Hi livinluvinlaffin,
Yes, you can definitely accomplish this but it is a fairly cumbersome process. To apply Auctiva templates to your existing eBay listings, please proceed with the following steps:
1) Recreate the listing in Auctiva and click "Save".
2) Once you have finished, click the "Save" button.
3) Return to your Saved Listings page, check the box next to the item, and click the "Get HTML" button.
4) Select All and copy the html in the popup window.
5) Go to the item that is active on eBay and click "Revise Item" then "Edit Description"
6) Click the "Enter Your Own HTML" tab above the description editor.
7) Delete the html that is already there and then paste the copied html in its place and save you changes.
It will probably be a daunting task to revise all of your existing listings in this manner in one sitting, so it may be a good idea to do a handful of listings each day.
-Mike