If you want to change from C to F or if you want to change the destination, it is not a change of the ticket. It is a cancellation and a new booking. Only if you change the date of the flight, but keep class of service and destination, it is counted as a change.
Changing a flight costs actually 25 Euro. A cancellation 50 Euro.
The risk is, when you cancel your booking and try to make a new booking, the miles may disappear instantaneously after the cancellation.