I don't think the link is relevant. Sign up to the Stay More Nights promo, and update your preferences by going into your account at spg.com. I'm not sure if a stay is then physically required to trigger this - but that should be all. There is nothing special about the link, it just takes you to the page to update your preferences.
I still would like for a Lurker to comment whether this was a targeted promo or not, i.e. for those of us that didn't get the email but signed up for the Stay More Nights promo and chose our Preferences, will we get the bonus?