The answer is maybe. In general you will not be penalized unless you are within 30 days prior to your ARIVAL DATE. The entire reservations is judged to start on the arrival date. The penalties that might occur for changes prior to the 30 days center around your use year, banking and borrowing points. Say you couldn't go in June but could in August or Sept. For some this would be in a different use year. So if you were using banked or borrowed points and your replacement trip were in the next use year, you would not be able to use any banked or borrowed points for the new reservation that were being used for the old one. That might mean you lose the points. Plus depending on when you made the change and a few other factors, you might or might not be able to bank any points to the next use year when you did change the date.
This is why use year can be an important consideration for some. For those that have a consistent travel time or times, they are best off with a use year that starts just before the time you usually travel. It just gives you far more flexibility if you do have to make alternate plans.
