Hello simonsezyeah -
I'm sorry to hear about the difficulty you've run into. Unfortunately it is not possible for us to update your saved or closed listings to utilize the new categories on eBay, we are unrelated to eBay and while we have updated our lister page to have the new category information available, our system cannot actually modify the already saved data in accounts.
Please understand that the lister page itself changes depending on the selections you make from the top down - for example, different options are available to you depending on the eBay Site you select or which category. When a category is selected on the lister page the options appropriate to that category become available to you - some of which may be required by eBay for a listing to post, but they are not the same across all categories. eBay may require an item condition or custom item specific that was not previously required and that information would need to be put into listings to be able to post, so often a change of category number also requires other changes to a listing.
I can certainly see how either of the options here may prove useful to sellers in similar situations to your own and encourage you to provide your request in our recently revitalized feature center (located HERE) where other sellers would have a chance to let us know their thoughts on such requests as well.
- Craig