How to merge-request an SSG blog post

On my own GitLab instance I am running a static website generated by Jekyll, which features blog postings. It is placed in the group www and the project is called www.website.org which is of course also the domain for the website. For testing purposes I forked the project into another group dev, and since in this group there may other projects be tested as well, the dev-website project is called just www which results the testing website being available on dev.website.org/www.

This makes it necessary to edit some settings in _config.yml, as there are:

-baseurl: ""
-url: "https://www.mywebsite.org"
+baseurl: "/www"
+url: "https://dev.website.org"

So in the dev repository I changed those settings, committed and pushed the changes into dev/www:master and Pages CI built the dev-website. So now both websites look the same, besides the dev being placed in a subdirectory.

Now I want to create a blog post, first on the dev-website, and then merge-requesting it to the real one. So in the dev-repo I create a new branch newpost locally, write the post, commit it and push the new branch to the remote gitlab repo. Then GitLab automatically shows a Create merge request-button in the dev/www project. But here it comes:

When creating that merge request from dev/www:newpost to www/www.website.org:master there will be both commits included, the blog post as well as the configuration update for the dev-website. Merging this will result in destroying the config file of the real website.

So how can I only merge this one commit? How does the workflow look like to do this correctly?