There was a similar question over on the Yahoo QTR forum. It wasn't clear to me whether you were involved in that. It also wasn't clear what sort of editing either you or the Y-QTR poster were looking to perform. For Piezography curves, mostly what you'd want to do is relinearise the curve, and the blog post goes on to describe how to do that with current technology. Not sure what else you'd want to do. On occasion I've had issues with the black ink limit on some papers, but I suspect that would be hard to deal with by simple edits to a .quad file. I've also had issues with ink overloading on a thin paper like EEM in the distant past, and had some success in dealing with that by hacking the .quad file to scale it down a little, but you'd have to be fairly desperate to try that. Other than relinearisation, the system is supposed to be plug and play.