I downgraded from 10.6.0-31U to 9.2.0-20U. It seems to be successful, but now I can't boot downloaded games that also have updates (only ones with updates that I have downloaded, not necessarily games that have the "update available" message).
I also cannot play games that "require" higher firmware than 9.2 such as LOZ Triforce Heroes. I tried HANS, but that didn't seem to work.
*Edit: It seems the the thing involving game-specific updates was a coincidence. In reality, the problem is with newer games (physical and digital). Is there any way to get around this restriction? As far as I know, these system updates are only for "stability".