Hey guys, in order to flash One X ICS V2.1 and considering you have bootloader unlocked and working over Coredorid One X ICS V2.0 this will be the steps to flash:
First of all, make sure your battery has charge enough to flash the rom 75% is the minimum recommended, then follow this instructions linked below to flash the boot.img file, VERY IMPORTANT:
You only need to flash the boot.img coming from 1.26 base, if a user already has boot.img from 1.28 base with the new kernel, flashing the ROM with boot.img will flash over fine.
http://xdaforums.com/showpost.php?p=24891132&postcount=5
Once you have flashed hboot.img, disconnect your phone from the PC, boot into recovery. Once in RECOVERY, follow these steps
1.- Select Install zip from SD Card and then select Zip from sd card
2.- Select the rom and then perform modifications
3.- Select on aroma installer what you want and what you don’t, when you are done and finished, do not reboot. Select “No” and select again the rom and this time perfortm a “One Click Update”, when done, reboot.
4.- Enjoy it!!!!!!!