Can UNESCO take a copy of Wikipedia (or, better yet, the list of "Featured Articles" on Wikipedia) and preserve that? Yes. Can UNESCO preserve Wikipedia itself? No, since, in this case, preservation is the same as destruction.
Imagine how much people in 500 years can learn about our culture by having a copy of wikipedia as it is now, and can look at its evolution over time.
Mostly it just means you have to get planning permission to sneeze and you can't have wheely bins or on-street dumpsters.
Heck, the organization is bureaucratic enough as it is right now (visit the Administrators' Noticeboard, if you want proof). Do we really want to be injecting UN levels of bureaucracy into that?
More often than not, the regulations would "protect" the house from home owners who wanted to perform renovations. There were many kinds of improvements that the owner of the house might like to make, but wouldn't be allowed.
I think this parallels the Wikipedia thing pretty well. Becoming preserved in this way cedes much authority to a third party, who can then dictate the kinds of changes that you may (or even must) make.
In the hands of an entity like the UN, I might even worry that steps might be taken to ensure that the resource that is Wikipedia be usable by all people -- and therefore needs to be sanitized of offensive content.
Unlike real estate, we will never run out of empty websites to build encyclopedias on. And, unlike a house, once you own a "free encyclopedia", you've invested nothing and can abandon it at any time.
If the world governments want to make a sanitized uneditable copy of Wikipedia, great. Nobody will use it, but it will make them happy. And that's what's great about the Internet.