Let me get this right, Spell Scars basically allows you to prepare extra spells (assuming you have the time - using scribe scroll rules).
You can either cast them straight off your body and then they're gone, or prepare spells for the day using them as if they were in your spellbook, thus increasing your repertoire.
Is that correct?
Do the scars cost the same as scribe scroll?
Can you prepare a scar at any level you can casts - like a 3rd level shield at 3rd level?
If one were using the Cabalist archetype where you become a spontaneous caster I assume the spell scars would effectively increase your spells known? or would you only be able to make scars of your known spells?
Also perhaps the scars would still be used up (vanish) if used, effectively increasing your spells known only on the days where you have had time/gold to create them? Or would you be able to keep using them indefinitely until replaced?