No, and it is worth saying why rather than just no. Opening a pack draws one specific card and takes it out of the pool — nobody else can draw it after you did. That cannot be reversed, so an opened pack is final.
But you are not stuck with the card. For the first ten minutes after you open it we buy it back at 100% of its market value, paid straight to your Harmony balance, instantly. Take that and you have lost nothing but the difference between what the pack cost and what the card is worth — which is a number you could see before you paid.
After those ten minutes the card sits in your vault and we buy it back at 95% of its market value on any day you ask. Not for a limited window: any day. So "I do not like this card" always has an answer, it is just not a refund.
An unopened pack is a different thing and can be refunded — nothing has been drawn.
The exception is ours, not yours: if a card arrives with the slab cracked, or does not match the certification and grade we published, that is our mistake and we refund it in full including shipping.