After your pre-authorization is automatically cancelled, the hotel will not cancel your room, because the purpose of pre-authorization is more to confirm the validity of your credit card than to withhold the funds in your card.

When you make a reservation, the confirmation letter you receive contains the price of Thai baht, which is the price when you check in. However, if payment is made in a currency other than Thai baht, the confirmed Thai baht price will be paid at the exchange rate of the day.