Gameflip had just released a discount code & I wanted to see if Im allowed to request a refund from the seller & re-buy the giftcard using the discount code
That would be up to the seller. If code was auto delivery and is given already, it is highly not possible because no sellers would want to risk it.
Only the seller could make that decision. If seller agrees to it, yes you can.
Understandable, thanks for the response!