I have printed out the DC postage for a book in a game.  I was thinking about mailing it from home so I was wanting to switch to pre printed postage.  Can this be done without incurring extra postage fees?

I am a little conused by your wording. I am thinking you paid for DC from PBS without postage. If that is the case, and the book is less than 13 ounces you could add stamps to cover the postage and DC fee.

If you want to use preprinted postage then you will get a new label when you purchase the postage and DC.

I did pay for DC without postage.  I was wanting to do preprinted postage but I already paid for DC.  I was wondering if they would discount if off it I used preprinted postage or would I be charged a whole new set of fees.

You should be able to tell by reopening the print wrapper page. Don't hold me to it but I'm pretty sure if you've already purchased dc, you won't be charged again for adding printed postage. 

You will be charged a new set of PBS fees.  Anytime we change the options we are charged a new fee. 

The tracking numbers are different for DC-only and full postage so you will be charged again.

If the book is less than 13 oz. you can mail from home with just stamps.