Here's something I dug up from another forum. If you know the basics of hex editing, you can edit the savegame file and look for, then change the following value:

List of known spells is stored in bytes starting from offset +1131. Each byte represents a row in your magic atlas. Value FF means that this row is not used. Value 0 is for spark, 1 for heal, 2 for freeze, 3 for fireball, 4 for hand of fate, 5 for mist of doom and 6 for lightning. Value 7 is for spell “Vortex”, which doesn’t work. Values 8 and 9 are for spell “Caustic fog”, which is the same thing as using green skull. It seems that those last two spells were disabled in game before release.