I went looking in the Gamefaqs.com forums for PS:T. and this is what I turned up:
http://www.gamefaqs.com/boards/18797...rment/49763875
Apparently, you can not unwrite a spell once you've placed it into your spell book. You can memorize and un-memorize to your heart's desire, but they seem to have not invented pencil for the puposes of copying and removing spells.
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