" The original is in overall good condition; graphics have an incredible gleaming paint but I´m afraid of a slight detaching tendency from paper base. The owners doesn´t consider to be worth to entrust the task to a professional restorer. "
I don't know if this bit of information will help, but if this is written on parchment, the ink is probably more fragile on the shiny, "skin" face of the sheet, where the ink couldn't penetrate as well. It probably penetrated better on the matte, "flesh" side where the ink could sink very deep. That's a thing to keep in mind when manipulating the manuscript. Also, consider side lighting if you want to preserve some of the skin texture of the parchment.