To clarify your question:
- You will make your booking before September 18,
- You will include dummy bookings for your flights after the wedding,
- You will take your first flight or two and then attempt to change the remainder of your flights to dates that you prefer.
Is this correct?
If so, it is a high risk strategy. Once you take your first flight, you can only change the date and/or time of your remaining flights.
You have to find availability on the exact same route, same airline, same class. What will you do if there is no availability?
Award seat availability to/from SCL and HNL is generally quite poor.
If you book the award before the changes in mid-September, your dummy flights are going to be around July. That will give you about one month to find availability on alternative dates.
If you can't find seats, you loose your points, only unused taxes will be refunded if you have to cancel.
If it were me, I'ld be booking the flights I wanted at the new points cost.