Interestingly a “restoration” of a damaged Rembrandt will typically not result in what the painter saw and oxidization and other degeneration will have changed the various paints in different ways over the centuries.

What is the appropriate repair point? Why should Violet-le-duc’s change be (or not be) privileged over more modern changes? The point of the building was to serve the people of a given time and it was adapted many times over the centuries to different usage models. Even the big plaza out front is relatively new (I have seen historical novels that anachronistically assumed the plaza to have been there, e.g. The Baroque Cycle).

When someone slashes a Rembrandt:

The replacement paint need not be absurdly toxic mercury compounds.

The backing might best be supported by something modern, such as a glass fiber mat.

Likewise with buildings, we can get the old style with modern materials.