Seems this guide, if not properly followed will cause a (soft)brick. Also there are more up to date guides.
In the interests of all users the guide is hidden, below.
If you wish to follow it go ahead. If you brick your handset, you were warned.
2: KNOWLEDGE OF ADB COMMANDS
PLEASE MAKE SURE YOU PAY ATTENTION TO EVERY STEP ON THIS TUTORIAL
***** I WILL NOT BE HELD RESPONSIBLE IF YOU BRICK YOUR PHONE*****
Make sure you don't have HTC Sync Manager installed, if you do uninstall it!! Also make sure you have HTC drivers installed!
Go here http://forum.xda-developers.com/show...76&postcount=6 and download the Argumentation's zip file
After downloading the PL83IMG.zip you will need to edit the android-info-txt inside. Please see sample picture below:
Now you have to place the zip file in C:\Android SDK\sdk\platform-tools folder. I know some people don't have the same directory as I have so this is just an example. Just make sure you place in the platform-tools folder.
Now connect your HTC One (MAKE SURE YOUR DEVICE HAS PLENTY OF CHARGE) to your PC and start a command prompt in the "platform-tools" folder. The quickest way to do this is (see picture below):
When you start your command prompt follow the steps in the picture below. PLEASE BE PATIENT!! After flashing the ENG HBOOT your HTC One will not boot up but you'll just get a gray spotted screen. Your device is not bricked. You can still use adb commands to write the model ID and CID even with a gray screen. WHEN REBOOTING HOLD DOWN POWER BUTTON FOR A FEW SECONDS. You might have to press and hold power button and volume down button when rebooting your phone.
You will not lose S-OFF and still have unlocked bootloader. I suggest that backup all important stuff before doing this I hope it helps.
If the mods feels that this doesn't belong here, please feel free to remove it. Thanks.
Here's a short video that shows how I changed my MID (model ID) on my HTC One