Agree with Dean. Even though many owners consider the transaction to be non-refundable, some will allow rescheduling within certain paramters. It really depends on what points will be used to secure the reservation.
As already posted, it depends entirely on the agreement between the owner and you. Be sure you ask and understand your change/cancellation options before you commit and send money. Policies will vary between owners. Know that Disney will not get involved in any dispute.
Best wishes -