Well, setmainverlow.zip flashed perfectly in recovery, but it still didn't allow me to get back to stock GB since I have a newer hboot.
I asked a guy that knows more than myself about it, and he said he was able to do it, but his phone is the Hero S on US Cellular. The Hero S is the same device as the Design, but it's branded for a different carrier and never received official ICS, so the process is probably different for us Design owners. In any case, I'll be in contact with him and we'll see if we can get it sorted for you.
In the meantime, I'll probably try to write up a more comprehensive guide for rooting the Design tomorrow because I see plenty of people asking about it and it'll be necessary for you anyway.
Hopefully, tomorrow will be a little more productive.
*Sent from work early bcuz some1 4got teh NSFW tag*