Steve - I've not had to replace vents on my WSM, but I've drilled out the rivets on the bottom vents of a couple of Smokey Joe Silvers. It's the same operation - drill out the rivet and replace with the new vent using a nut and bold - or if you have the right sized rivet driver, I guess you could do that.
It wasn't a terribly difficult job, but make sure you've got a good drill as it does take a little time and effort to drill out the rivets.
Good Luck!
Pat