Changing the first flight after ticketing is a reissue, so that is a special case. "Local service fees may apply" for a reissue, although there is no charge in the fare rules. If it were not a reissue then I suspect many people here would use this facility freely in order to get in ahead of price changes, fuel tax increases, etc without knowing when they actually wanted to start the trip.

On all other segments you can change without charge.