Although it might seem like an unnecessary topic, but someone might want to revert back to Android 4.4.4 KitKat from Android 5.0 Lollipop. Several reasons come to mind – you might not like the material design, you might experience performance problems with the Lollipop or you might want to go back to the stock firmware of your region instead of using the GPE firmware or the Brazil firmware. No matter what, you might want to go back to KitKat. Follow the steps below to do that. Please be cautious that this might soft-brick your phone and the way to un-brick it is to flash the lollipop firmware again.
For some reason, you might want to downgrade your HTC One from Android 4.4.2 to Android 4.3. For example, I updated my AT&T HTC One to Android 4.4.2 with Sense 6.0 by converting it to Developer Edition. After using it for some days, I wanted to revert it back to stock conditions. You might want to do it before returning it to AT&T for warranty or other issues. If you just try to flash a lower version RUU, you will most likely get error message. The problem results from the fact that higher Android firmware from HTC usually comes with a higher version of HBOOT. So, whenever you try to flash an RU.exe, it will show you error as it cannot flash a lower version HBOOT to a device which already has a higher HBOOT version. We need to manually flash a lower version HBOOT first and then use RUU.exe to return to complete stock.