If you still have time left on your warranty, taking your HTC One in for repairs can be a serious pain if you've modified it in any way. To avoid the chance that they'll reject your phone because it's been tampered with, you'll have to return it to stock condition.
To Do This, You'll Need to S-OFF
Not only does this let you install the ROM Update Utility (RUU) that will restore the original firmware, it lets you get rid of the messages in your bootloader and splash screen that say your HTC One has been unlocked or relocked.
As a cool bonus, S-OFF (which stands for Security-OFF) can also... more