No. We don’t send reservations to the hotel until late February. If you call the hotel before then, they won’t have your reservation on file. Additionally, hotel staff is instructed to send you back to SXSW Housing to make your changes online.
The only exception is changes made within 72 hours of check in. To ensure the hotel receives last minute changes to your reservation and you don’t have trouble checking in, it is best to make those changes online and call your hotel to alert them of the change, particularly if you won’t be checking in on your reserved check-in date or are arriving very late.