The Rebel Yell hasn't been heard in quite some time in person from someone who actually had used it in battle, and that might just be one of the things that fades away into the history books. That is just one of those things where "You had to of been there" kind of deals to get it spot on.
I hate to be the bearer of bad news again..... but I have never crossed paths with a Private First Class or Staff Sergeant on either the Confederate side, or Union side in my 10+ years re-enacting..... maybe some of the Regiments should switch those out with a real quick "Google" Civil war ranks search.

A Veterinary Sergeant or a Saddle Sergeant is more period then those.