Complete Arcane has rules for alternate spellbooks, including tattoos (P. 186-187). While this is less economical than just putting on a Ring of Regeneration, cutting your fingers off and carving the spells into your fingerbones (either 1 page for a tattoo on the hand, or 1 page per finger bone), I'm curious as to how the magical tattoos can work alongside changing the caster's body so that the skin becomes empty again. Can you use this to store more spells on/in your body, and maybe somehow remember them? Or when you wipe them out you lose all knowledge of the spells you had and you'll have to tattoo them again?
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In short, you really can't get extra spell pages by changing your form.
The longer version involves some not-terribly-well-defined rules. To my knowledge, there are no rules about what happens to tattoos on your body when you change your shape. Based on a careful reading of the shapeshifting rules, I would say that any tattoos on your normal form would remain when you shifted back into that form, but the wording is not 100% clear. In the end, whether your tattoos go away or not will be up to your GM.
If your tattoos go blank when you shapeshift, then any spells you have scribed on your body go into a weird limbo state, where you know the spell, but don't have it available for preparation. Assuming that you don't have any other copies of the spell in other spellbooks, you can no longer prepare it. You might be able to talk your GM into letting you gain access to it through Spell Mastery, since the language about what happens when you know a spell but don't have it in a spellbook is pretty wonky.