It seems the generally accepted view is that you can't rebuild wings of your manors in game without uninstalling Hearthfire (the second poster at http://gaming.stackexchange.com/questions/103728/how-do-i-reset-my-manor-so-i-can-rebuild-it-with-different-options says differently, but that just led to me deleting the meshes of the wings without allowing me to rebuild anything in their place), but I was wondering if there are any mods or workarounds that allow you to do so? I'm sure this is a much requested feature!

Thanks in advance.

Could have sworn if you went to the drafting table you could switch them or at least reset it to that small cottage thing.

Nope, as far as I know you can't switch them. It even says in the book about building houses in-game that the decision is final. I think the option you're thinking of converts the area of the manor that begins as the small house into a foyer of sorts.