timfountain

I've never had a problem tell the hotel on check in that my requirements have changed and I will be checking out on such-and-such date. As long as I am 48 hours out, I can't see that they have a leg to stand on.

writerguyfl

Sometimes the hotel's desired outcome is to get you to cancel. Any outrageous price (in money or points) is a way to discourage new bookings without setting the hotel to "sold out" status with the chain. In both (non-Hilton) chains in which I worked as a Revenue Manager, once you invoke "sold out" status, there are financial penalities if you end up not selling out.

Without access to data, it's impossible to know exactly why this hotel is asking for that many points per night. My educated guess is that they are oversold and they are not going to turn around and resell the night you wanted to give back.

Check the fine print on your Hilton reservations. You should see this text:
That's a pretty strong leg, to me. Although, I'd bet most Front Desk agents aren't trained to re-price the booking based on current prices.