Unfortunately I could not find a way to do that with eBay or Auctiva bulk edit just for 20 items last night. I dread a related category change which could result in 200+ items having to all be changed individually. In fact the eBay bulk edit to relist kept hanging because I could not change the category from a now deprecated rail book to a non-fiction book.
Looking at the category threads on eBay boards eBay does not give a damn especially to sellers using store inventory format, they want only auctions. It think it was late last year they significantly reduced the visibilty of store in searches and recently hid the option for store searches off of the default options available from an initial search. You now have to customise the search display to even get store searches shown as an option.
Auction only sellers appear to be far less affected than inventory store sellers by these category changes, as turnover is faster.
I have already added a bulk edit of category request to the suggestions board. Please add you thoughts to that thread, we need help and Auctiva is probably the only one who is likely to assist.
Apologies for the rant, I try not to but this situation caused by power crazy mega-profit eBay is really aggravating me and seemingly many other buyers, sellers all over.