How do you make a custom pack in Sealed Deck?

The packs from the original and the hacked packs (8th, 5th, Legends, Chronicles, etc) Have all been mismatched with replaced cards and added cards that don't belong in that set. My question is, is it possible to make new packs to use in Sealed Deck, and how do I make them? I know this is possible because of the 8th, 5th and Chronicles packs taking certain cards from each of the 6(7?) avalible "sets".