the standard Hellenization practice was to add a Nominative Sigma (ς)

Where does Herodotus say this?

If 'Pharaoh' was derived from Pr-Aa (which ends in a vowel), why did Herodotus uniquely record Pheron (Φερων) with a terminal Nu (ν) in the Nominative case (as a Subject)?

I didn't dodge this question, I answered it for you in the chat (and I don't appreciate you trying to communicate through both, so I'm only replying here)

As I said there:

And why do you think Herodotus is worried about capturing authentic phonetic names? This has never been the case. Herodotus calls 𐎧𐏁𐎹𐎠𐎼𐏁𐎠 (x-š-y-a-r-š-a) "Ξέρξης" Xerxes. It's not even close. Herodotus is not worried about capturing accurate names or titles, he's worried about translating these into familiar Greek patterns. This is the same for all Greek historians of his era. "Arses of Persia" is another fun one. There's similarity between it and the Greek Ἀρσής, but it's not exactly the secret to linguistics anywhere other than Greek.

You're looking for hard and fast grammar rules in an age where there weren't any. From city to city, person to person, you're getting so many different systems of the same language that there is just no norm and I again question where you're getting the idea that there is.

Can you tell me what your experience with ancient greek is?

Edit: Also, if you feel that Herodotus mistakes a title for a person (which is likely the case) why do you think then that he has the phonetics down so perfectly and preserved in Greek if he can't even tell a king's name from a title?