I've bumped into this scenario a couple times, it's a rarity so it was never a big deal but one instance where this would be useful would be something like a fundraiser page. I can't use a global block because every fundraiser is different.

At the top of the page I've got a Fundraiser Goal block where the admin can enter an amount with just a regular content block.

At the bottom of the page, I'd like to just repeat that content of the Fundraiser Goal and then put like a donate button or something.

This way the admin only has to edit the one block to update both locations. I'm sure I've read a how-to on this a long while back in 5.4 but google has been fruitless as has poking through the documentation. Well the documentation gave me ideas...

I imagine I need to grab the page ID (maybe not since it's the same page?), then the block name and contents and any template it may be using... and then, display it??? The reality of me actually writing the PHP for this though is something else. I pretty much know enough PHP to be dangerous but not especially... inventive :P

Thanks for any input!