(assuming you're working with raw files)
Even if you actually saved the original using either the Ctrl-S(quicker) option or the File->Save option and saved the original raw file, you can always go back and re-edit this file back to its 'original state' if you like.
So don't be afraid of editing the raw file .. even if you think there is some importance in maintaining the original raw files pure integrity.
This is the beauty of raw files .. no matter what you do to them .. as long as you use that same software, you can mangle them to death .. and yet maintain the ability to restore them back to their original state if need be.
I'm curious as to the a, b or c suffix on the file name too tho.
If you're renaming the file, then by default you'd be saving to a new format .. unless your original format is tif or jpg of course, and you're saving to the same format, which makes perfectly good sense.