Dev accounts are now limited to 50 Devices unless they are proven big developers already. They are then limited to 250 devices. It used to be 1000 across the board.
You do not need a UDID to be registered for this to work. You just need to download the .ipsw and force restore by pressing Option and clicking restore at the same time on a mac or Ctrl and restore on windoze in iTunes.
This will then ask for the location of the .ipsw and you select the iOS 7 that you download.
Google is your friend for the .ipsw. Be aware they are Circa 1.2gb dependant on phone/ipad model to do a full restore. OTA updates are 115-214mb for beta 3