As always, test test test. I tried this for BCC, repeatedly, and never got it to work.

Also as always: do not assume that you're seeing the result of any one element unless you are testing that element in isolation. You might think the lightbox element is the most prominent aspect, but the call to action also changed from "Start Optimizing Your Website" to "Create A/B Test ->"

You see that arrow there? That arrow, tested in isolation, has been worth 10% to me before in some circumstances. Yeah, it blows my mind, too. And there were many other things that changed.