I need to hack my PC built game .assets files - but how?

Here's the story:

I accidently replaced a prefab with another prefab object, and then I had to redo everything to make it just like it was before, but I'm having trouble with that.

I used that backup restore Windows 7 thing, but unfortunately it doesn't affect any documents.

I have a whole archive of PC built unity games of it, before the prefab was screwed up.

My question is that: is it possible to decode/hack into the .assets file or whatever, and retrieve that prefab again? http://answers.unity3d.com/questions/10879/is-it-possible-to-hackdecode-asset-files.html talked about it, but they didn't tell me how to actually do it.

I have no clue how to recreate it, and my archive PC-Built games have my prefab when it was working correctly.