To correct a home folder whose name has been chaned

I think OS X has something similar to the Windows Safe Mode, and it also has a command line only mode. If you boot to the command line only mode, you should be able to execute a single simple command to change things back... It would be something like the following:

mv /Users/<NewName> /Users/<OriginalName>

Just replace the bits in brackets with whatever the directory name is now to what it was before you messed with it. If all goes well, everything should be back to normal. If not, all hope isn't lost.

OS X has this handy option when reinstalling, called "Archive and Reinstall". It basically just dumps the entire contents of your drive into a subdirectory, and then reinstalls the OS. So you don't lose any documents, and should be able to just drag and drop programs from the Applications folder in the archive to the new Applications folder. You may lose some settings, but most apps should work.