Just dug into it – this is actually built into WooCommerce – you are normally expected to manually edit a product to change the default attribute, but we have altered it so you can set a default and it applies once it is saved.
You can automatically have this apply to all your products at once by checking the Update Licenses? checkbox when you edit a license. However, due to the limitations of WordPress, depending on the number of products you have, this could take some time and/or hang. You can run it multiple times in the hope that it will get through it, and you can also deactivate the processor temporarily while it’s going to increase the probability that it will finish. Let me know!