If some one don't know how to reset the Main Quest line, this doesn't means that is not possible,
So let me up this thread, there must be something !
No there mustn't.
You've already been told why this is physically impossible. If you were able to reset the main quest, the game would have to reset every item, NPC, dragon, shout, discovered location, etc. that was involved in the main quest.
And I'm still not sure why you want to do this in the first place. There's absolutely no point.