When creating a spellbook for a hero to use (Inspires Me to do a mage!), just create a new ability that is based off "Spellbook (Item)" and change it to your will. Allows you to make a simple spell book with 1-9 spells max I think. Allows you to also change what spells/how many it has per level:
Hero has a skill called "System Defence (Spellbook)
Lvl 1: Only has spell "Bit Guard LVL1"
Lvl 2: Spells "Bit Guard LVL 2" and "System Lockdown"
Lvl 3: Spells "Bit Guard LVL 3", "System Lockdown" and "Web Shield".
Note this was just an example of what can be done easy with spellbook ability.
I've tried this before, it doesn't work, you have to do somerhing to the MPQ, whenever you try to level it up or put most spells in it and cast them, you get an illeagle operation...
Here see my test map. Also has a few other things like some terrain but that was just a test... The cryptlords have the "System Defense Options (Spellbook)" and it does work. The summoning ritual does nothing but still try it out. It is not protecte so you can look at it.