The downgrade (from F to J) was notified on the 15th Feb for a flight leg on the 24th Feb. The notification was by email but I did not see it as I had already left the Uk on the outward leg by then and had not checked that email address whilst away. I therefore only become aware of the downgrade when checking in at BKK for the return. I filled in the online refund form on my return to the Uk on the 24th Feb. Refund was in my credit card account about a week after submitting the form.

There is a picklist on the refund form that allows you to select downgrade as the reason for your refund request. Also I dont believe that you need to do anything about changing your flights, just turn up at the airport with your original reservation and accept the downgrade when you check in, then after the flight fill in the refund form. From my interaction with Emirates staff on the phone it would appear that they have no control over downgrade refunds and everything needs to go thorough the online form to a dedicated team.

Hope this helps

Trotski