[Desire HD Android Development] attn1:
Yes, this should absolutely work on your japanese DHD.

yes, the docs tell you the radio is downgraded, then an appropriate radio is reflashed. Read better. After using the hack kit, people are free to flash other radios if they really find it necessary. Most do not. Most users who do flash different radios do so not because of issues, but because someone else told them to. I am not packaging up every conceivable radio when two will do (one GB and one Froyo). The radios flashed at the end of the process are both AT&T radios - and are both good performers and later radios on their respective platforms.

Yes, radio, boot (incl kernel) and recovery are downgraded to expose the exploit. Later, they are all replaced with suitable versions. Your kernel is nothing special - and is replaced by a boot image containing a correct kernel for your device and should work fine with your build. Again, I am not going to pack up every possible boot image when a few will do. If this approach is bothersome, you can flash your RUU without losing s-off and have a stock environment. The options menu will then allow you to flash CWM without altering anything else. Then you are free to flash superuser to an otherwise 100% stock rom via CWM. The holy grail here is really S-OFF. With that, you have control of your device's configuration.

Returning to stock is not as simple as flashing the RUU however. S-OFF with remain. The hack kit addresses that too, for some builds. Unfortunately, Softbank is not one of them - yet. Thanks for the link to the GB RUU, I'll use that to add softbank to that feature.

The OP says it is also compatible with RELOCKED bootloaders on Sense3 ROMS.

I am not going into the merits of S-OFF vs the HTC bootloader and what other methods there may be. This is the hack kit thread, and I only care to discuss things pertinent to the hack kit. I'll only say there are other methods out there - but don't flash an ENG or Froyo hboot on a device shipped with GB.

Placing adb and fastboot in /bin simplifies troubleshooting and means they are available later. Permissions are fine. I really don't care if you don't like it - you are free to remove them later or use your own method, which I won't support.

adb and fastboot (particularly fastboot) do not work reliably without non-root execution without modifying config files. This gets tricky in automation. Running as root works across popular linux and OSX platforms.

You say adb works - fastboot doesn't. Well no, fastboot is not required, but it simplifies the process when it works, which is why it is default. Not all Linux distros are created equally, which is why I strongly suggest people use the 32 bit Ubuntu LiveCD over any other PC configuration or installed OS. If fastboot doesn't work on your PC, then you can use the alternate flash method if you are absolutely sure of your adb connection.

The download is not prohibitively large, the effen manual is fine where it is. I prefer to maintain it in one place - the hack kit. To be honest, I think the hack kit makes this easy enough as is. if you don't like what you see - fine. Move on. I don't care and you won't hurt my feelings.

Both of these questions are answered when you do the required reading. That version can be downgraded but the kit to a generic version, and then yes, the hack kit can be run again and work. The SDCARD is not cleared normally, but corruption can occur in a small percentage of cases. The manual is clear that you should back up important data before beginning.