not carved in stone

Those terms are not carved in stone, however.

Kazaks added that initially the ECB should raise rates by 25 basis points but this increment is not carved in stone.

Because effectiveness must account for real-world variables, it’s not carved in stone.

There is a mountain of evidence that the political alignment of states is not carved in stone.

As in monumental sculpture itself, perspective is everything: the faultiness of what we call art history, with its false dream of meritocracy, reflects the limitations of the people who create it; it is, after all, not carved in stone but a living chronicle to be reinterpreted, blasphemized, blown up and rewritten.