I tried downgrading my n3ds from 9.9.0-26U to 9.2.0-20U and got an error during the process.
EDIT:
Since I didn't have any of the recommended things, I thought I would just try to run sysupdater again. It had trouble starting up, but on the 4th or 5th try I got it to boot and pressed Y again to downgrade. This time it went through to the end and rebooted the system after 10 seconds.
So it looks like if you can run sysupdater you don't need Zelda and another 3DS to fix this problem.
now my log file is much shorter:
Code:
Title ID 0x0004003000009e02
Extra title
Title ID 0x0004013000001b02
Expected version 0x0800
Installed version 0x0c01
Title ID 0x0004013000001a02
Expected version 0x1400
Installed version 0x1801
I think I should be good now