I would be very surprised if the devs switched your houses, something that (to my knowledge) they've never done for anyone. I think when the GM recommended posting on the forums, they meant that you should petition for a general fix that the devs might eventually add somewhere down the line. I would not count on such a feature being added any time soon. Most likely, the only way you're going to fix this problem without waiting a very long time, is to save up enough money to repurchase both plots.

If you do wind up demolishing and repurchasing the plots, make sure you wait a couple of weeks for this housing rush to die down. Give another member of the FC buying/building privileges so that when you demolish both houses, you can buy the small plot and the other person can buy the large plot for the FC.