How could I import a production website into a home-computer localhost virtualmin, and make it behave as if it were still up?

If your website is WordPress, there is another way…

Lookup wp2static plugin for WordPress. It allows you to develop the website in one location, and upload a static version of it to another.

So you set the static version as your production location, whilst you play around editing the dynamic version on another directory, or different webserver altogether.

Obviously this has its limitations.

Another option is to configure your Windows hosts file so that if you type a domain name into your Web browser, Windows goes to a wamp/xamp directory on your system itself…Ie your browser doesn’t go looking for external dns for ipaddress for this website (This method should work, however you will need to remember to change/disable it when you want to view live production site online)

https://docs.bytemark.co.uk/article/testing-a-new-site-by-editing-your-hosts-file/