Setting up a Mirror Site for Backup/Migration

My site is at https://www.solacesystems.com on one web host.
I duplicated the site at https://www.solacesystems.biz on another host.

I plan on migrating soon by switching my .com domain name to the new version of the site, but for now I want to treat the .biz site like a backup/mirror.

I exported the xml from the old site and imported it into the new, but apparently new versions of existing pages don’t overwrite. Is there any way to set it so they do? Or any other way to automatically or efficiently port the contents of one site to another even covering instances where an existing page is being updated?

I found this but it’s way over my head.
https://blog.namran.net/2009/06/07/automatic-backup-content-from-wordpress-to-another-mirror-site/

Thanks for any ideas.