Just to backup what emusan said . . . except I'm going to be a little less tactful . . .
Editing the build.prop is a pretty safe operation. As long as you do everything right, changing the device fingerprint isn't going to mess up your machine. Reading through your posts, I can't help but feel we were missing some information, which really prevented us from helping you. I mean, you were able to boot well enough to install ROM Manager? And to realize that the permissions in your apps were messed up? When did that happen?
Finally, the reason for editing the fingerprint has nothing to do with "getting the market to work." Playing with the fingerprint might affect the kinds of apps you see in the store. The market uses the fingerprint to determine the identity of your device and then filters the available applications. If you check the store again, you might notice that your app selection is limited (or maybe not, but this is certainly what people have reported when using other tablets).
Finally, I'm mystified as to why your restore won't work. Certainly, all of us can't anticipate having that kind of problem. As I said, I've messed this thing up twice, and I was easily able to revert back to Dingo and then update back to Ermine. The fact you are having trouble with that procedure sucks, but the only reason I included those instructions is because I figured there is always a way to restore the device; in your case, that happens to be false, but that's not anything I could have predicted. There has to be something pretty serious wrong for your device not to properly restore.