Hi,
I'm going to guess you're wanting to add templates to active listings. That's not something that Auctiva can currently do, i.e. they don't support a method through the API service with eBay for that type of code revision.
Here's one current method you can try for migration. Auctiva can IMPORT closed listings from eBay. That's done on the Auctiva Closed Listings page. That feature will schedule (give it a few hours if it doesn't happen immediately) and bring back the code from closed listings and place them in an Imported listings folder which you can access from the Auctiva Saved Listings page. From the Saved Listings page, you can edit individual saved listings, BUT there are also bulk edit tools including the ability to add a template to a selected group of saved listings. Organizing your Saved Listings by Folders (move from Import to whatever) can help segregate those you want to bulk change e.g. by categorey (or type of template). I would experiement first to see what can easily be done by Import and bulk change with maybe a few selective listings. Once you have a method (step-by-step) estabilished, it should go a little easier.
Hope those tips help.
Danno