I think this is a typo There is no such thing as rare charms. I'm sure Noodle meant rare Jewels here.Can you reroll rare charms? Yes, with six perfect skulls. Please note the level of the item will drop. Magic (blue) items are the only ones you can re-roll without decreasing the item's level.
No , I meant using a simple magic weapon/charm/jewel with the recipe and getting a rare/unique weapon/charm/jewel.