What happens if I replace the files of a WordPress site with another WordPress site?

🤷‍♂️

It depends on the functionality provided by the plugins and theme.

For example, there could be differences in database schema that some plugins and themes depend on.

Even if the site doesn’t break right away, you will probably miss functionality in your site and be left with a bunch of junk data and/or code.

It’s not a good idea to do this. I can’t imagine a time where you would want to do this.