United Airlines - Changing non-refundable ticket to refundable and then cancelling?

[clay]

Is this a legitimate loophole or am I missing some catch that will make this impossible?

If you did do this, I doubt you'd get a full refund to your credit card.  Chances are, the refunds would go back to the "original payment method."  So, the newly spent money on the refundable fare would go back to your credit card, but the amount of the original tickets would probably go back to a flight credit.

this is kind of what I was expecting to happen if attempted.