[Sprint HTC One (M7)] jbhtexas:
I was able to get a PRL downloaded to the HTC ONE with the KitKat 4.4.2 stock ROM from CDMA Workshop. In order to do so, it was necessary to make a small change to the htcdiag.inf file that is part of the HTC Diagnostic driver. This change is described below. I was working with Windows XP SP3 32-bit. The procdure can probably be adapted to Windows 7. You will need CDMA Workshop (trial edition works) and a set of HTC diagnostic drivers. I would recommend making a backup of the phone and the htcdiag.inf file.

PLEASE NOTE THAT YOU USE THIS PROCEDURE AT YOUR OWN RISK. WORKING WITH CDMA Workshop CAN POTENTIALLY DAMAGE/BRICK YOUR PHONE IF YOU ARE NOT CAREFUL. INSTALLING FAULTY DRIVERS MAY DAMAGE YOUR WINDOWS INSTALLATION. YOU ARE RESPONSIBLE FOR ANY DAMAGE TO YOUR EQUIPMENT.

1. Dial ##DIAG# (##3424#) on the HTC ONE, and select "YES" to enable diagnostic mode. If you a trying this on a different phone or different ROM, diagnostic mode may already enabled after dialing ##DIAG#. This should cause Windows to present several prompts for installing drivers. Cancel all of these requests.

2. After this, open Device Manager, and you should find the "unkown" devices shown in the attached image xd1.png. The HTC ONE presents two devices "HTC DIAG" and "HTC 9K DIAG". For the ONE, I could only get "HTC 9K DIAG" to work. For the EVO 4G LTE on Android 4.4.1, only the "HTC DIAG" device is presented, and it does work.

3. Right-click on the "HTC 9K DIAG" device, select "Properites", and then the "Details" tab. You should see something similar to what is shown in attachment xd2.png. Note the part of the Device Instance ID inside the red box.

4. Find the htcdiag.inf file in your set of HTC diagnostic drivers. In my driver set, this file was located in the "Win x86" foler. The version of my driver is shown in attachment xd3.png.

5. Locate the [Strings] section of the inf file, as shown in attachment xd4.png. Note the variable assigned to "HTC Diagnostic Interface" . In the case of this inf file, that variable is "OEMDevice02".

6. Locate the [Models] section of the inf file, as shown in attachment xd5.png. Find a line in this section that begins with the variable identified in step 5. Copy this line to a new line in the [Models] section. Modify the Device Instance ID portion of the copied line to match the portion of the Device Instance ID inside the red box as described in step 3. Save the inf file.

7. Right-click on the "HTC 9K DIAG" device in Device Manager and select "Update Driver..." The steps below may vary a bit, but ultimately you want to get to the point where you can select the htcdiag.inf file modified in step 6.

6a. Select the "Install from a list or specific location (Advanced)" radio button, and click"Next"

6b. Select the "Don't Search. I will select the driver to install" radio button, and click"Next"

6c. Select "Show All Devices" in the listbox and click "Next"

6d. Select the "Have Disk" button and click "Next"

6e. Select the "Browse" button, locate and select the htcdiag.inf file modified in step 6, and click "Open"

The driver should now install if the inf file has been correctly modified. You will have to ignore the complaints about the driver being unsigned.

7. After the driver is installed, you should see an "HTC Diagnostic Interface" in Device Manager's "Ports" tree, as shown in attachment xd6.png. The "(COMx)" portion indicates the port that will be used with CDMA Workshop. From this point, the procedure documented at http://xdaforums.com/showthread.php?t=1673490 can be used to load the PRL of your choice. Be sure to reboot the phone after installing the PRL.

This worked for me. Given the fickle nature of computers, it may or may not work for you. Thanks!