You can restore the original firmware but to flash it you have to open up the console so unless you can keep the warranty sticker from being voided (I tried very hard and it still voided, some people have done it though) then the warranty is dead anyway.
Many games now are stealth patched and ixtreme is supposed to be pretty safe for stopping you being banned but, its always a risk.
I have to say also that once you flash and start with the backups, it kinda ruins the 360
. Wanting the games with a passion, buying them when you got the cash and playing them =
. Downloading, burning and playing = fun for a while but its only a short while and then youre downloading the next game =
.
I actually regret flashing my 360, I wanted it for so long, loved it and now....not the same. Still love it though
.