That's a far-fetched claim, of course, as editing of live video streams it not exactly a trivial task, regardless of whether it is on the Internet or elsewhere. The RIAA also claims that the stream could have statements “edited in” and then passed off as the original, which could be damaging to them. It's all nonsense, of course, and it is clear that the RIAA wishes to avoid any publicizing of the trial to avoid the world seeing just how they portray themselves in court.
I hope the webcast goes on as planned, as many others would. It would be interesting to see what exactly the RIAA does in court. Given the opportunity to see such a trial, would you tune in and watch?