Welcome to the forums bholmes4.
I would suggest the same as Lightseed. Just let them take out a spell or two, and add some in as they see fit.
Say, one player who plays the wizard, really does not like the card Mana Leach, and wants to put in a fire spell of the same point value. Just set mana leach aside and switch it back out when they are done.
Really, in this game, its not so much what spells you have in your book....its what you do with them. (And when you do it.)