I wouldn't try this in Japan... it is an extremely "rules oriented" society and you are not likely to get away with it. They will ask you for ID and when you fail to present it, they will charge you the rack rate. And don't bother with the "dumb gaijin" tactic either... everyone at the Park Hyatt speaks perfect English.

Even though its nowhere near as luxurious or service oriented, the Hyatt Regency down the street for the Park Hyatt is an excellent hotel and can usually be had for 1/4 the price. With the extra $$$ you save, you can have a wagyu beef dinner every night at the New York Grill at the Park Hyatt.