In 2013, more Android devices will receive Jellybean updates, but most likely will have 4.1 firmware versions instead of the 4.2.1. HTC One X+ users will not expect just an update yet of Jellybean 4.2.1 version, so CyanogenMod developers provided a stable Jellybean 4.2.1 firmware.
Here is the sum up of the update using CyanogenMod.
All data in your device should be turned off in the middle of the firmware update. The steps below will guide for any back up. One reminder: Do not back up HTC One X+ using a ROM manager to avoid bricking.
SMS - Use "SMS backup & restore app"
Contacts - Sync with Gmail
Call log - "Call log and restore"
Multimedia and data files - Copy to internal or external SD card
APN & MMS Settings - Note down from the path "Applications > Settings > Wireless and Network > Mobile Networks > Access Points Names"
Make sure to check this path: Settings>Applications>Development>USB Debugging. Enable the USB debugging and ensure that the USB debugging option is ticked.
Battery Level should not be below 30% or there will be risk of damage to the device during the firmware update.
Turn off all antiviruses in the computer to avoid interruption during the update. Double check that the USB Read/Write rights in the computer is enabling.
Follow the instructions carefully and do not perform acts that are not included in the procedure to avoid bricking the device.
Steps to Update HTC One X+ with Jellybean 4.2 CyanogenMod 10.1 Firmware