Yes, rooting does technically void the warranty, but on the N7 it is completely reversible.
Your best option is to root, install GooManager and then select Install RecoveryScript from the menu in the top right. This should install TeamWinRecovery. Then you can do a full system backup from TWRP.
You can do the same with ClockWorkMod Recovery, but CWM does not back up the kernel so you have to restore the backup and then flash the kernel or the ROM.
Otherwise just use Titanium, but that is a PITA hitting Install on each app that gets reinstalled.