Downgrading HTC HBoots has been all the rage this year. Users usually do it so they can downgrade to a HBoot that can be S-Off unlocked. They aren’t the most user friendly procedures, though. In many cases, doing so involves hard bricking the phone and using either Qualcomm’s download mode or a wire trick to bring it back to life, flashing an old HBoot in the process. There is now a similar process for AT&T HTC One X users who are brave enough.
XDA Senior Member yarrimapirate has released a toolkit that helps get your HBoot downgraded to 1.09 for further hacking. While the toolkit seems like an all-in-one solution, there is a lot more going on under the hood.
This is essentially the same method as linked above. The tool bricks the phone and uses download mode to flash an older Hboot. Then, it recovers the rest of the phone. Users who are willing to try this need to be running Linux and need to have a good deal of patience. In some cases, this can take a very long time to work. For those who encounter problems, yarrimapirate includes a troubleshooting FAQ.
To learn more, check out the original thread.