'External keys' are itch.io's way of letting you distribute keys for other marketplaces with an itch.io purchase. We support Steam or keys of your own format. You can bulk add thousands of keys at a time. Previously, when adding keys, if you made a mistake then you would need to contact support to modify the keys you've added. Starting today there's new a Key management section that allows you to remove keys individually or remove all unclaimed keys:
You can find the Key management tools by clicking View all next to any set of keys you've uploaded.