Hey folks, I just wanted to warn that AT&T might still 'catch' you for using tethering without a plan. I used a similar method via the X-Tether Xposed app, and after some heavy usage I got an email, text, and letter in the mail from AT&T letting me know that my plan didn't have tethering (grandfathered unlimited plan) and that if I continued to use tethering, they would adjust my data plan accordingly. They were kind enough to give me a warning before shutting me down, but please be aware. I also had KNOX disabled as best I could find to do so using Titanium, and still got the alert. I used the native Wifi Tether app.
EDIT: This was a situation unique to having the S5. I previously used the popular Wifi Tether Router app on my Skyrocket, and previous phones, for about three years prior to getting my S5 without any notification from AT&T.