You can always just RUU - that's directly from HTC and will get you completely up to date. You just have to back up your data first.
P.S. Once you root your stock ROM, that makes it a custom ROM, you know .
P.P.S. Since you won't be able to take an OTA without losing your data, you might as well relock and RUU anyway. Then you can unlock, flash the latest TWRP, let it root for you and be up and running on the latest update.
Saw your response and had to ask... I installed the latest OTA, S-OFF and rooted. I made a prior backup of my data with TWRP but whenever I restore it, I end up in a boot loop on the HTC One white screen. Phone works fine as long as I don't restore my data backup which sucks. Any advice you can offer? threads i should read thru?