[Q] Unlocked S5 --> Cyanogenmod Flash - will it work/remain rooted on AT&T? topic

I would love to run a non-stock android ROM (cyanogenmod) on a Samsung S5- my question is if I buy an unlocked galaxy s5, root it, flash cyanogenmod- once I put it on the AT&T network will it brick? Would I be better off trying to get a "developer edition" of the phone that I've read about?

(sorry I feel like this questions has been asked thousands of times, but Ive googled for hours and cant find it)