If you didn't make your own backup, or use an editor that saved the original as a ".bak" file, you had better just use Steam 'verify game files' option. And then get in the habit of making backups of any file you mod. (This process is documented in the 'Steam and mods' wiki article.)
Something that can actually save you time in the long run is to copy what you want to change to a simple text file, and make your changes there. Then copy-and-paste into the actual file when you are satisfied with your changes. That also can give you a record of what you changed if you add notes to your text file. But backups are always recommended.
-Dubious-
Edited by dubiousintent, 21 November 2013 - 08:48 AM.