I'm not sure how it works with a
DCL reservation - but I believe the rooms are in a specific block.
If you did want to try for a request, you'd have to note the requests on your reservation. Most resorts are now ignoring the faxed room requests because they've become so overused.
You can still try faxing, but I would do that in addition to noting the request on your reservation. The reservations are sent from the reservations center to the hotel 5 days prior to arrival, so I would do it 5 or fewer days prior to your arrival.