[HTC One S] Candlemass:
Thank you for your answer and congrats on your ROM (it is the one I'm running right now ;) ).

I managed to solve the issues yesterday, but the information was so scattered around, it took me half a day (along with the sloooow downloads).

For anyone interested, the procedure was like this :

1) Unlock bootloader via htcdev.com and identifier token

2) Flash TWRP 2.6.3.0

3) Root

4) SuperCID

5) S-OFF

6) Change CID to HTC__001

7) Update HBOOT to 2.15 via firmware flash

8) Run newest RUU

9) Flash newest radio

10) Re-flash TWRP

11) Flash Custom ROM

Step 8 can be skipped, but I wanted to see if it ran the stock ROM ok.

In more detail, with links and files :

Initially the phone was branded on 3UK with CID H3G__001, HBOOT 1.06 and MID PJ4010000.

version: 0.5
version-bootloader: 1.06.0000
version-baseband: 0.15.31501S.19_2
version-cpld: None
version-microp: None
version-main: 1.53.771.4
serialno: HT242W411761
imei: ***
product: vle
platform: HBOOT-8960
modelid: PJ4010000
cidnum: H3G__001
battery-status: good
battery-voltage: 4018mV
partition-layout: Generic
security: on
build-mode: SHIP
boot-mode: FASTBOOT
commitno-bootloader: 802fa374
hbootpreupdate: 11
gencheckpt: 0

The safest way to update my HBOOT to 2.15 or 2.16 was via a latest official RUU from here http://www.androidruu.com/?developer=Ville . But the latest RUU matching my CID was a bit old (RUU_Ville_U_H3G_UK_1.78.771.5_Radio_0.16.31501S.19_2_10.23.31501S.10L_release_258982_signed) and I didn't know which HBOOT it contained, so I decided to update using the latest European RUU (RUU_Ville_U_JB_45_S_HTC_Europe_3.16.401.8_Radio_1.11.50.05.28_10.27.50.08L_release_301814_signed_2_4). In order to do this, I would have to chance CID to something corresponding (i.e. HTC__001 or HTC__N34 for my region - ELL).

(1)

I began with the thread [Tutorial]Root, Unlock, Recovery and flashing a Custom ROM, but got stuck on the recovery flashing, that's when I started this thread. I flashed the latest TWRP (2.7.0.0) and latest CWM (6.0.4.8) but they didn't work.

The recovery boot acted as described in the OP (gave me the generic HTC recovery screen) and tried multiple times. Then I remembered reading something like that the newest recoveries work differently to support newest hboot, so I tried the previous version (TWRP 2.6.3.0 from http://techerrata.com/browse/twrp2/ville ) and it worked.

(2-3)

TWRP also offered to root the ROM by installing supersu automatically, so I didn't have to flash it myself. After the reboot to system, I installed supersu from market, updated su binary and the root access was complete. The rooting was necessary so that we can change the CID to SuperCID.

(4)

SuperCID can be set following this guide [UNLOCK] AT&T Bootloader Unlock Through HTC-Dev. I changed H3G__001 to 11111111 with HxD (needs care not to change more that those 8 bytes and check that the size remains the same - mine was 1024B).

(5)

Next stop is S-OFF via Facepalm with the help of this thread	[S-Off] Facepalm S-Off for HTC Devices One S, One XL, Droid DNA. It worked right away, following exactly the procedure as described.

(6)

I changed CID to HTC__001 , not leaving SuperCID on, because there were reports of bricks when flashing OTA updates. Just wanted to be on the safe side.

Easy from fastboot with S-OFF :

fastboot oem writecid HTC__001

(7-8)

The next step was to flash the latest RUU (RUU_Ville_U_JB_45_S_HTC_Europe_3.16.401.8_Radio_1.11.50.05.28_10.27.50.08L_release_301814_signed_2_4), in order to update my HBOOT to 2.15. But this came to a halt, as the RUU didn't proceed, giving me error 159. More info and solution on this matter can be found in the thread RUU_Ville_U_JB_45_S_HTC_Europe_3.16.401.8_Radio_1. 11.50.05.28_10.27.50.08L_release.

In short, the problem is that the ROM.zip inside the RUU is encrypted and we either had to decrypt it using ruuveal via linux, or to use the already decrypted by hasoon2000 zip ( http://xdaforums.com/showpost.php?p=40925380&postcount=79 ).

As I also mentioned in that said thread ( http://xdaforums.com/showpost.php?p=52852710&postcount=123 ), if you update the HBOOT manually, by flashing corresponding firmware, the RUU flashing proceeds without any issues.

So, I followed the thread [GUIDE][TOOL]FUU/FirmwareHTC One S and flashed the Official Unbranded 2.15 Firmware (Sense) zip via fastboot. The result was an updated HBOOT to 2.15 and the ability to flash the official RUU. With S-OFF there is no need to relock the bootloader.

(9-10-11)

After that, I simply reflashed TWRP and the custom ROM Liberty-S4-V7a. I skipped the manual radio flash, because Liberty ROM had the option to flash it from AROMA installer automatically. For other ROMs, it is a simple flash via fastboot.

Simple, hah :p