Hi Everyone - I just spoke with CS with regards to this specific question.
They told me:
If a guest requests a change of dates for a later set of dates - if the request came during the no refund window of your cancellation policy - if you accepted the change - then the cancellation policy will reset to the new dates as if it is a new reservation.
So if after reserving the new dates the guest later decides to cancel - they will receive a refund (or not) based on your cancellation policy relative to the new dates.
So this is a way that a guest can cancel without paying any penalty - working around your cancellation policy.
Be wary of accepting a change request like this which can expose you to a double loss. The guest can cancel the revised reservation just before the no refund window opens and in doing so have caused you to miss other guests reservations for BOTH the original and revised reservation periods.