Well, apparently the freely distributable boing bags are considered "warez." (Am I only the only one that hasn't used that word since he was 12 years old?) And if you were unfortunate enough to install BB2's buggy devices, well, I guess you're just screwed. ;-) Maybe you could try contacting Amiga, Inc. Oh wait, they don't give an eff about their customers, so no luck there. :-P
I think the official OS 3.9 FAQ has some info about rolling back files as well, but I wouldn't want to be accused of copyright infringement by posting a link to it.
So, here's what you do:
1. Back up your data.
2. Format your system disk.
3. Install OS 3.9 from CD.
4. Install BB1.
5. Back up any files you don't want to upgrade.
6. Install BB2.
7. Restore the files you didn't want to upgrade.
8. Restore your data.
9. Reinstall your applications.