I want to share my experience about revert to stock for users that have new HBOOT, unlocked bootloader and custom recovery; can't execute official RUU. ( This method i think is more safe that downgrade HBOOT )
Install this custom ROM: MaximuS ROM ( read the thread for instruction about installation of this ROM )
( this ROM allow you to receive the message of OTA JB update, if you know another ROM that receive this message you can use as well i think )
install the stock recovery of HTC One S via fastboot ( after flashing recovery erase cache )
Reboot your phone in system, configure the rom for first use, go to settings, information, software update and press check now for update.
You'll receive the message for an update, download and install, and now you have stock JB ROM. after reboot you can do a reset ( go to setting => backup and restore ) to clean the application migrated from previous ROM ( MaximuS )
I hope this can help someone else.
p.s. Sorry for my English!