Voice Master Calling Card question

I have a very small question regarding our VM when we want to increase our card values. Right now forexample I have made a batch with 6000 5 dolllar cards and activated 1000 of the cards. From these 1000 cards activated, a few around 200 are and have been used. Now I want to increase the face value of the remainder of the cards to $6 as promotion. I was wondering how i can do this without increasing the face value of all the cards even the cards in use and used; so only the 800 remining cards that are active go up from $5 to $6.