Generally there is nothing illegal about altering a legal document, or even a strict definition of what counts as a legal document. Under some circumstances it could be illegal to alter a document and use that for fraud, or submit an altered document to a court or government agency. If the doctoring falsely defames someone then you could also open yourself up to a civil suit.

OK, and could you detail this "procedure"?

Because to me it seems like altering and disseminating a document would be under 1st amendment protection, unless combined with some action that e.g. causes someone else harm or tricks the state into doing something it should not do or something.