there is a gateway between the media center canbus and the critical canbus. the gateway buffers all the data from the critical canbus and rate limits any requests for data which isn't broadcast regularly on the critical canbus.

You would have to get UID=0 on the canbus gateway to make requests 'willy nilly' on the critical canbus. Having UID=0 on the media centre would only help in making willy nilly requests to the gateway.

edit: clarity