Mandatory Facebook Friends? Utah apartment complex says yes!

The Associated Press has a story about a Salt Lake City apartment complex that's notified current tenants of a change in their leases. The change requires them to "friend" the apartments on Facebook. Note "The document also has a release that permits the property to post pictures of tenants and their visitors on its Facebook page." 

So, my questions: is there an ethical reason for such a rule? (Personally, I'm shuddering over the idea that photos of kids and other residents could be publicly posted.) 

Can landlords legally modify a currently-running lease? I thought we had to wait until the lease was renewed, or new tenants move in.

See http://abcnews.go.com/Weird/wireStory/likes-salt-lake-city-complexs-facebook-requirement-39467912