I find interesting that both the example you gave are places for the dead. In contrast Notre Dame is still an active place of worship, and it would shock me less to see change to it. A similar but more secular example would be the glass dome on the Reichstag building in Berlin.
Today's Great Pyramid is much different than what the Great Pyramid looked like when it was first built, according to the TV programs I've seen. There used to be an outer layer of white limestone on the pyramid.
Relatedly, when I was young, Notre Dame was black from years of pollution from the industrialization period. They cleaned it up and restored its original stone color.
The Ancient Egyptians were also like us in that they were into architectural bling and greenery, so I'm not actually sure they'd be complaining that much. They were into materials like gold, electrum, and polished stone, but I'm sure you could sell them on modern glass.
That said, the Great Pyramid is a historical site, not an active worship site, and modern archeological sensibilities prioritise conservation. A restoration like that might make it hard to answer future questions about the pyramid.
I’m not worried about offending the ghosts of the ancients. Let’s try another analogy: if the Mona Lisa were damaged, should we “improve” it with “modern bling”?
