Hi! Thanks for asking, but you won't need to buy a specialization to recover Newt's Patronus spell, since it's just one spell that he already would have known and was voluntarily nerfed. If the new movies introduce significant new magic beyond what we already know about that you'd like to add to his power set, that might require a specialization purchase.

However, we would need to discuss what effect a Patronus Charm would have in Thedas, since scaring off all demons or something would be a bit OP. So if/when you decide to de-nerf it, make sure you talk to us about that.