I DO NOT GIVE REFUND/REPLACEMENT FOR CARDS HAVE BEEN TRANSFERRED/ADDED TO/FROM A DIFFERENT CARD.
Also, do not combine all of your cards into one to make a lump $500 gift card. Starbucks card system will detect it and automatically close your card because you are transferring a huge amount at once. You will have to email Starbucks about this and explain what you did and they will replace your balance back in your card.
I advise you to keep the balance on the original card and do nothing else other than get your heavily discounted coffee from it.
I only give refund/replacement to cards with the original balance on it !