They can't void the warranty either way. Look at the top of the maintenence guide. It says it is "recommended" to follow the maintenence schedule. Not "required/mandatory". I can't remember off the top of my head, but I remember that the individual items in the schedule use the word "should" when it talks about replacing/changing items, not "must".

Of course, it's a good idea to follow the schedule and replace items as deemed necessary. Just know your rights if the dealer tries to void your warranty.