Dear Stephaniesonline,
No, it is not currently possible to add a listing to a consignor after it is active but we will be adding this functionality to the Auctiva website with a future release. At this point, it seems pretty likely that we'll be able to get this functionality in place for our next major site update, which will take place in April.
Any additional questions or concerns? Please contact our customer support department using the appropriate link on our help page:
http://www.auctiva.com/free-auction-software-help/help.aspx-Mike