Yea I think this would require rooting. And to be more specific it is a guide to how to get VoLTe to work and not 4G
This is all fine as long as you know what you're doing. A "plain mortal" like me, who is not doing this kind of work but has different occupation in life, would not dare to do it. I would still love to have VoLTE.
Guides are made so that we "plain mortals" can do stuff like that.
You got the tencent model and he has got the international one. You probably have gone through a fair bit of playing around with the working files in the phone to convert your firmware. so you probably won't feel as...apprehensive as him ?
Still I wouldn't dare. I would like to try those actions first on some old device to get a hang of it. Doing something for the first time is always a risk. After some practice I could do it also on a new phone. But I expect Asus will some day do it for me and provide me with VoLTE. But of course this is just my opinion.
First time for everything
It's better to live one day as a lion than a thousand years as a lamb.