Probably not, depending ont he final wording of the court decision a reasonable demonstration its the same site the same ruling could be applied without going back to court.

Surely such a demonstration would require another court order, though? If not, who is to judge the extent to which two sites are the same site?

If the Newzbin source code is released — and to be clear the issue here is not the software itself but what people do with it — and a hundred Newzbin clones pop up overnight with entirely different branding, domains, hosting arrangements, etc., surely one court order against Newzbin is not enough to force ISPs to block all of them?

To reiterate, the software behind Newzbin is entirely legitimate. Passing a court order that enables blocking orders for all websites using the same software would be akin to one that enabled the blocking of all Wordpress blogs because one such blog had been used for illegal purposes.

The thin edge of a very large wedge indeed...

Yeah it would depend on the wording of the final decision. But courts aren't stupid, and criminals trying to alter behavior to side step a ruling is nothing new either. These cat and mouse games have been going on since laws started.

There's a project called Newznab directly written for the purpose of allowing people to set up indexing sites easily.