[Q] HTC One X+ Stock Rom WITHOUT root topic

Hello,

I've just bought an fresh new HTC One X+ 64GB :) (last stock from HTC probably, it was very cheap , just 150€)
It bring the ROMv4.1.2 that I like very much :):)
Somehow the phone gets updated via WI-fi to ROM v4.2.2
The reason why I post again this topic is because I've searched and searched to revert to v4.1.2 and always read the word Impossible!!!
The phone heats a lot, the battery lost capacity and I HATE HATE and HATE the ROM v4.2.2.

The question that I leave here to you guys, is really IMPOSSIBLE TO revert to Original ROMof my phone WITHOUT ROOT?

As the phone is quite new, I don't want to lose the warranty!
I've seen a lot of videos on youtube saying stock rom without root, but they use the fastboot, that it seam to be the ROOT!

I've rooted already my Samsung ACE2 and updated using Odin, but on HTC I'm quite newbie.

Can anyone help. :confused:

thanks in advance,