While I’m in sympathy with the conclusion I’m not sure about the reasoning:

“If it was technically possible [to remove an image painted over another] it would certainly be unethical, as it was Magritte himself that decided to cut up one of his paintings and then create new compositions over the fragments,” she said.

“The preservation of the artist’s intention is in my opinion our main priority.”

“Non-invasive and non-destructive imaging techniques will enable us to make a reconstructed image of the hidden painting.”

Creators’ intentions and wishes have come up before—Kafka, Nabokov, Vergil...—but those cases involved unpublished work (enabling appeals to privacy, or to a desire not to be remembered for unfinished compositions), along with the intention that it should never be made available for public viewing... which is clearly not the intention being honoured here, as the third sentence shows. Favouring non-destructive imaging because the painting on top has some (ethically salient) worth of its own would be a familiar form of argument. Even an argument from posthumous harm might be more easily linked to destruction of the artist’s later painting. Reifying intent and setting it up as the thing you most want to preserve... I’m not sure what to make of that.