Originally Posted by
Horace
Think of it just like a cash reservation.
Forget about points for a moment. Let's suppose that, this week, you reserve a a hotel room for 5 nights beginning May 1, 2019, at a rate of $300 per night. Early next year, you decide you want to arrive on a different date. Your modified reservation will be at whatever the rate is for new reservations and it will subject to whatever availability there is at that point. You cannot depend on being able to move your reservation to a new date range at the same hotel for the same room type at the same rate.
It's the same with points reservations.
However, one trick that can *sometimes* be helpful is to consider booking each night separately if there aren't minimum stay rules for your dates/rate or if you're not eligible for the fifth (or Nth) night free. Then, for example, if your flights require you to change a stay for May 4-8 to May 6-10, you can keep the nice low rates for May 6th and 7th that were available when you made the original booking. If May 8th and 9th aren't prohibitively expensive by then, you've scored!
ADDED: You can later, when they actual dates are confirmed closer to arrival, ask the hotel to arrange for you to stay in the same room or to merge the reservations, even if you have different rates or rate planes for different dates. Hotels want to do this do that they don't have the housekeeping cost of you changing rooms every night. It will count as one stay regardless. At the very worst, with elite status you check out after the check in time for your next reservation, but it would be rare for a hotel to do this to you.