I am not sure if there is a way to do it within the website, but you could do it using the api. You would need to load each coin in your collection & then edit them to change the for swap change. The script shouldn't be too complicated, but would take 4 months, as there is a 2000 call limit per month. You might be able to download your collection with the item IDs which would mean it would only take two month.
I wrote a script to import my collection (only a couple of months to go now) which might help you - you can see it here:
https://github.com/pwclay/NumistaImporter