Move test site changes to live without losing live posts

Hello! I have searched and searched through Google and the forum here for answers to my questions but I’m afraid I haven’t found them. Please forgive me if I’ve missed it, I really just need another human to ask! ??

I have a client who wanted to update his WordPress site, so I made a copy of it an moved it to another server for development. Moving the site and databases back and forth went fine, but when I moved everything from the test site back to the live site, the changes that were made to the live site after I made a copy of the site were gone. So for example:

June 1 – copied live site files and database, moved them to development server.

June 1 through 14 – client continues to post on his live site while I make changes on the test site. He also added a plugin and some new categories.

June 15 – move changes (which include new pages and categories) from test site to live site. Everything is beautiful, except that the posts and categories he added June 1 through 14 are gone, and while the plugin still exists, it is deactivated and all of it’s settings have been lost.

Being some what familiar with databases and the move process, I see why this happened. My question is, what can I do to add these posts, categories and plugin settings back in after I’ve updated the live site?

I know I can use WordPress exporter and export the applicable posts from the live site before I move the changes over, and then import them back in after I update the live site with the changes. This is ok right? Problem is the featured images are not exported/imported. How do I fix that?

What happens if I try to import a post with one of those new categories he added and the new category is still non existent at the time of the import? Will the import create the category and then add the post? Or just add the post with no category?

(I don’t think using the “all content” export option would suffice because wouldn’t that overwrite the changes I made to pages and navigation menus when I import it back in?)

How do I get the new categories and plugin data back in? I am comfortable inserting rows directly into the database but in all the searching for this answer 1) I don’t think that would work and 2) if it did I’m not sure I know which tables I would find all of the applicable data in.

Are we basically left with trying not to make too many changes to the live site while it’s being worked on in another environment? This particular client runs a news site so he’s updating content constantly.

I appreciate the assistance!

Thanks – Lori