Hello, is there a way to modify the hardness of the block?

The example on the wiki is :
onEvent('block.modification', event => {
event.modify('minecraft:stone', block => {
block.destroySpeed = 0.1
block.hasCollision = false
})
})

What is the meaning of block.destroySpeed ? Let the player dig slower or faster？But it does't work for "block.destroySpeed = 10".

I want to change the hardness of the block， I write as the below，but it does't work.
onEvent('block.modification', event => {
event.modify('minecraft:stone', block => {
block.hardness = 50
})
})

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