The change fee vs/ cancel and make new reservation fee will vary, on how knowledgeable the CM is. I have been told I cannot change, and that I have to cancel for the $100 fee, and start over, by 2 different CMs. I have also been told I can change for the $60. It all depends who you get.
I read that the CM make their commission on new reservations, so many are going to tell you that you have to cancel the old, so that they get credit for a new reservation, IMO
It just totally burns me up, the different answers you will get from the CMs. My experiences lately are more to the negative side, when dealing with the agents. I haven't come across too many that are knowledgable, or even polite. We have been going to Disney for the past 12 years, and have never encountered so much wrong info.