Honest question: If I own the copyright to a webpage (say my personal blog) and Comcast modifies my page to insert this "helpful" warning message, is it likely I'd have a case to sue them for creating an unauthorized derivative work of my content?
Since they are making a new derivative work without the authorization of the copyright holder, they are probably guilty of copyright infringement. The remedy for that could include statutory damages for each work they infringed of "a sum of not less than $750 or more than $30,000 as the court considers just"[1]. However, since the infringement was patently willful (they published an RFC explaining their intentions and methods), "the court in its discretion may increase the award of statutory damages to a sum of not more than $150,000."[2]