Question [Q] Root while on AT&T Next?

So I ordered this phone yesterday and I want to try some custom roms on it but I don't know if rooting while on Next would be a safe idea. I'm positive i can root and flash a rom with no problems but if i wanna switch phones in 18 months will I still be able to?

If it just needs to be the way they shipped it, will flashing a stock rom and un-rooting do the trick?

Thank you all in advance, and keep up the great work. Happy rooting.