you can for some. One, you have to train the original spell (like you have fire elf) or if you spent the training points in storm, you would have kracken. Then check out the bazaar and look at the treasure cards under the Charms section. There are mutate cards in there that will mutate spells you know.
i am a lvl 34 pyromancer i have had monsters use other chools spells as thiers like fire kraken, fire zilla, ice elf, ice kraken why cant fire and ice get those spells? i mean the monsters can