Reworking Broadway Musicals

I had always thought that once a Broadway show had reached its opening night performance, that was it.  The show was frozen.  Sure, some shows have some natural sections of improvisation in them, like the current production of The Addams Family, which allows comedienne Jackie Hoffman to ad-lib many of her lines.  But Variety Magazine has recently come out with a great article about how, sometimes, shows are reworked over the course of its run to keep it fresh.  Here's a link to the article on Variety's website.

http://www.variety.com/article/VR1118021067.html?categoryid=15&cs=1