Reprepare Spell

You've discovered how to reuse some of your spell slots over and over. You can spend 10 minutes to prepare a spell that you already cast today, regaining access to that spell slot. The spell must be of 4th rank or lower and can't have a duration. You can reprepare a spell in this way even if you've already reprepared that spell previously in the same day.

If you have the arcane thesis, you can instead prepare a different spell in an expended slot, as long as the new spell doesn't have a duration. You can use spell substitution on that slot again, but you remain restricted to preparing only spells without a duration in that slot until the next time you make your daily preparations.