Have your coworker write out 100 times 'I must not undo that which I have not the knowledge to redo'.
Then go see a conservator.
Just to make your coworker really miserable, read him/her the following quote from a conservator:
"Because of the nature of animal skin, parchment and vellum objects have acutely hygroscopic properties and are liable, even over a very short period of time, to unevenly change shape in all dimensions. This obviously produces serious problems when trying to hold an object in a certain position within a mount or frame without damage occurring. Expansion and contraction of parchment and vellum through environmental fluctuations, can have disastrous effects on an object, especially if movement is limited at certain points because of attachment to a mount or backboard. A very common form of damage caused is cockling. This symptom can cause destabilisation of areas of pigmentation and gilding, resulting in problems such as flaking pigments and the cupping, tenting and loss of gilded areas. Obviously, if an object was kept in an ideal and most importantly consistent environment, (55% relative humidity 20'c temperature) there would be little, if any, movement and consequently little opportunity for damage to occur. Realistically however, an object's environment cannot always be controlled to such an extent and so, a certain amount of compensation must be allowed with regard to expansion and contraction."
And of course, have the coworker pay for both the remediation treatment, and for the conservator to perform the correct mounting procedure.