What is the problem with interpreting this rule?

It is as clearly as possible.

"Do not make any changes to your estate until after Sponsor reveals the winning entries."

And in the context of the contest it is clearly stated that they are meaning the interior of the house/private chamber.

For comparson the german version:
Verändern Sie Ihre Unterkunft nicht, bis der Sponsor die gewinnenden Beiträge bekannt gegeben hat.
Translated this means:
Don't change anything at your housing till the sponsor reveals the winners.