No, because you have to RMA an item (GPU) with all the parts that came with it, because you will more than likely not get the same GPU back that you RMA. No, because the serial number label is attached to the back plate on ASUS GPUs that come with a back plate. However, if you purchased the GPU without the back plate, take it back to place of purchase.
I could be wrong! Anyway, you can try to do a RMA. You're only going to get one of two answers from ASUS: Yes (it will cost you more money) or No. Let us know how the RMA process worked out for you.