[HTC One S] Rapier:
Latest radio for WWE devices was 1.15 and it's not a problem you have that. For me it proved to be better than 1.20 which is coming from the leaked firmware 2.16 so it's unofficial. You can't flash a different radio unless you're S-Off or have a lower hboot (1.09 or below) which you don't have. Stay with 1.15 it is OK

If you're S-On you MUST flash the ROM kernel EVERY time after you flash a ROM. This is done by extracting the boot.img from the ROM ZIP and flash it via fastboot command (fastboot flash boot boot.img). Also no nandroid restore will flash back the kernel from the backup since it is not possible to write to that partition if you're S-On

Now, what options do you have... First you must decide WHICH ROM do you want on your phone. If it's latest Viper you would like, fine, it's a very good ROM, stable and with lot of customization and support. What you should do is like this:

1. Download the ROM, save it on your pc and check MD5 sum

2. Extract the boot.img from it. This is a little bit tricky since Viper use an Aroma installer and it's made for both 2.15 and 2.16 hboots. So the boot.img is not in the ususal place in the zip file (that is the root of it) and also it is not called plain boot.img. It is located somewhere in the ZIP folders (sorry but I don't use Viper and don't have the zip at hand to tell you exactly where to look) and it should be named something like boot_2.15.img (or something like this). Look into the ZIP and try to locate this file, you should find 2 files named similar one with 2.15 and one with 2.16 in their names. The one you need is the one containing 2.15 in the name. Extract that one on your pc

3. I assume that you have ADB/fastboot working and you can launch the fastboot command from any directory on your pc (it's in the PATH). If not it could be that command will not work. In this case copy the extracted boot_2.15.img in the folder where you have fastboot (usually Android-SDK/platform-tools) and open a command prompt there

4. Restart the phone in recovery and mount the USB storage from it. You should see it after a while on your PC. Don't worry if it doesn't appear instantly, but it shouldn't take more than 1-2 min. Eventually unplug the phone and plug it again into USB. If you cannot mount the USB and have it accessible from PC we have to try the ADB Sideload but first we'll see if you get there and we need this. For now I presume you can mount USB and you can access it from PC. OK, now copy the ROM ZIP on your sdcard in a folder you'll remember

5. Now flash the ROM in recovery as you normal do and wipe cache/dalvik when prompted to

6. Restart your phone in bootloader and plug it in the USB. Go to fastboot and on screen you should see "FASTBOOT USB". Issue on the pc in the opened command prompt the command "fastboot devices". It should return the device id and that's the proof the device is recognised by the fastboot command. If you have returned an blank response or something like an error, check if drivers and everything on your PC is installed properly for fastboot to work

7. If "fastboot devices" returns something (should look like "FA2BGW... fastboot") then you're good to go. Issue from the same command prompt the command "fastboot flash boot boot_2.15.img" (replace boot_2.15.img with the actual name of the file you have extracted from the ROM zip)

8. Restart to system

At this point you should have Viper 3.1.0 flashed and working. Check and setup the ROM then you may want to download the 2 OTA updates and install them to get to the latest 2.1.3

let us know how it went and where are you stuck. Note every error message you might get and better ask first than be sorry later...

Good luck