"Your disguise is barely hanging on by a thread."
paraphrasing " your disguise is Rock Solid, make sure to set your disguise name attribute."
My gameplay experience is that even with the first message of the disguise barely hanging on by a thread, I have been able to get in combat without having the disguise slip. I have also had fairly extensive dialog with other characters over the course of many minutes and not had the disguise slip.
Given that, my suggestion is that we add a middle tier status message. Something along the lines of, "Your disguise is decent."
To me, barely hanging on by a thread implies that if I dare to do anything other than simply walk from point A to point B, my disguise is more than likely going to slip. The reality is that I can do much more than that.