I misunderstood it seems.
There isn’t any way to copy values from an existing post to another existing post.
Any solution would have to be custom built based on the needs of the client and what is being copied.
As an example you could add a true false field or some other type of field that allows setting what to copy or where to copy it to. The you could create an acf/save_post field that checks these fields that then does the copying.
The main issue you’ll run into is scalability. Copying date across posts would take time and likely time out if there was a lot of copying to do.
A better solution would be to have a options page, or if the values are based on categories to have custom fields on the categories rather than individual posts. Any time identical values will apply to more than one post it is best to store them somewhere other than for each post.
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