I also got a schedule change. My outbound flight was cancelled and the new outbound flight offered was after the return flight.
Anyway I called the service center and they informed me they can re-book the ticket to a new date but only within ten days of the original travel date.
If I wanted to travel later, I would need to deny the schedule change claim the voucher and then book a new flight.

I shifted things around and 'rebooked' to travel one week later. The ticket endorsement does state: INVOL REROUTE VALID ON A3 FLIGHTS ONLY.
The e-ticket lists as fare basis the old fare code. In addition there is: PR60. I assume this is to indicate the promotion that I booked.
I really hope this change does not count as re-booking. I did ask the service center if the mileage promotion still applies but the answer was rather ambiguous.
They only mentioned nothing changes and I do not need to pay anything in addition.