Carved/set in stone
Definition 1 of 3
Pro Tip 1/3
Changeability
Used to emphasize the potential for change in rules or plans. Although our itinerary looks final, it isn't carved in stone.
Pro Tip 2/3
Expect Flexibility
Indicates that, unlike literal stone, the subject can be adapted. Your job responsibilities are not carved in stone and can evolve.
Pro Tip 3/3
Metaphoric Use
Used figuratively to represent rigidity but does not involve actual stone. The schedule is set in stone for now, but we can review it later.