The charging of credit cards is something handled by each individual hotel. In theory, most hotels wouldn't mind charging you now...even on rates that are not advance purchase. They'd get your money 4 months early and pre-paid bookings are less likely to cancel.
That said, some properties may opt out of it can be a hassle to refund the money if the reservation is canceled. In one hotel where I worked, our Accounting Manager didn't like charging cards ahead of the stay because the hotel would lose money if canceled and refunded. (There's a very small cost to process the charge and another to process the refund.) I always chocked that up as the cost of doing business. But, she cared. So, that's one reason why hotels might not pre-charge credit cards.
As
OriginalName writes, you'll need to contact each hotel individually during their normal business hours. That can be a hassle.
Another option would be the use the Contact Us feature on the Hilton website. Create a separate message for each hotel and put "Please Forward this to Hotel" at the beginning of the message. The message will get sent via Hilton's internal communication system. Each message is tracked and hotels will have a pre-determined time to respond. Hotels can't say they didn't get the request, like they could with email.
Link to Contact Us Page:
https://secure.hilton.com/en/hi/feedback/index.jhtml