Hi helmetbabe,
Auctiva does not provide any tools that that would aid in the revision of active listings so you would need to make these changes in your active listings using eBay's revision functionality. I'm not sure if eBay offers any tools that would help you to make this particular revision in bulk, so it may be a good idea to check with eBay's customer support team about that.
If you would like to edit the return policy in the saved listings stored within your Auctiva account, you could do that using our "Find and Replace" functionality as long as it is feasible for you to apply the same checkout information to all of your listings. If you would like to do this, the first thing you would need to do is create a checkout profile containing the checkout options you would like to apply to your listings in bulk by clicking the "Checkout" link under the "Profiles" tab.
Once you have done so, you would then need to go to your Saved Listings page, check the boxes next to the items you'd like to apply your new checkout profile to, and then click the "Find and Replace" button. On the ensuing page, you would then select "Checkout Fields" from the first drop-down menu you are presented with and then select the specific checkout profile you created from the one that appears thereafter.
If you have any additional question or concerns, please feel free to contact our customer support team by completing the web form on the following page of our site: http://www.auctiva.com/help/requesthelp.aspx
-Mike