I also finally managed to downgrade from 10.3 (US) to 9.2 on an o3ds XL
For a while I was stuck with a line 100 error: could not read CIA information.
This error:
The fix was simple enough: I just re-extracted the CIA's zipfile using a different program. I couldn't tell you what to use on Windows, but for OS X, using The Unarchiver, rather than the system's unzip utility helped.
Obviously, after unzipping, you need to copy the new files over. But after that, it was quick and painless — even rebooted!
So maybe put that in the op for the few people who've had issues?