All you need to do is contact them and they will reset the devices back to zero. I have to do this every couple of months, as after window 10 updates it always seems to see the computer as a new device. 
I wonder how it is going to work with chromecast, as when you cast to a chromecast, you could potentially cast to multiple tv screens that have a chromecast, so potentially you could have 10 difference devices being cast to, even though there is only one device registered. Maybe that is the reason for the delay in chromecast support. It wouldn't be great if the chromecast support required that the device was always connected to stream it, eg mirroring rather than true casting,  as it would run down the battery on the device very quickly.