I don't know where you read such "informed" info but the proper way was to copy/paste the icon in the finder get info window. You should never tinker with the apple provided drivers (kexts) and I guess now you know what can happen if you do.
You most likely got the kext cache out of sync probably along with the finder realted cache(s). Also, that kext is code signed. That alone was enough to screw it up (see reference link).
If candybar is actually doing that then IMO consider it malware (a) for the reason I stated earlier about no one (or thing) should be tampering with apple provided software and (b) if apple ever updates the system with an update for that kext then it will be replaced with the apple updated kext thus invaliding the previous edit.
Code can easily recompute a bundle's code signature so if candybar is screwing around with the kext it could just update the code signing. It wouldn't be the first time some 3rd party utility did such a thing. I believe there's one that changes the appearance of OSX by changing a whole bunch of OS X stuff. It think's it's kosher because it has an uninstaller that puts back the original stuff it clobbered. Pretty insidious IMO. Maybe candybar is doing the same kind of crap. But in both these cases it won't get around a apple system wide update that potentially could revert the stuff these utilities clobbered.
(At first I want to say that my English is not that good, so there may be some faults in this anser.)
I had the same problem when i did the same thing as you did.
I changed some icons (so it would change all the drive's icons instead of one "via get info..."), and got the same issue.
After I searched for the solution on how to reinstall the .kext, I came up with this site.
after following the steps, it fixed my problem, but the only down thing about this is that you need to have a backup (eg. a Time Machine Backup) to get the "IOStorageFamily.kext" file from before you made the change.
I provide you with my .kext file. (I do not know if this will work for other machines yes or no, but I think is is the same for all Macs.) I would first try with your own backed up file.
I have a rMBP 15" with OSX 10.8.3 in case.
I hope this will fix your problem.