I hoped I wouldn't have to, but unfortunately I'd like one of the "in-dev" games I just purchased refunded if possible. Supposedly there's a 14-day "no questions asked" policy on those? How do I apply for the refund?

Support ticket. Not sure if it has it's own category.

Go here:
https://www.gog.com/support/contact/my_orders_and_payments

Select "preorder cancelation" as the problem type and explain in the fields below that you would like to have your in-dev purchase refunded. Make sure to include the order's number (which can be found here) to speed up the process.