From reviewing another post on here:
It looks like you're able to submit a sitemap through Google Search Console. My only question is if you, later on, decide to take it down does Shopify re-autogenerate the default robots.txt file?
Thanks in advance,
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This is an accepted solution.
Just a quick update about the robot.txt file that was referenced in this post. As of today, June 21st, 2021, we have launched the ability to edit the robot.txt file to give merchants more control over the information that is crawled by search engines. You can learn more about how to edit your robot.txt file through our community post here.
To directly answer your question, if you create your own robot.txt file, then choose to remove it, then the default robot.txt file that Shopify provides will be used. Sitemaps can be updated manually by following the guide you linked in your post.
If you have any questions about the new feature, please do not hesitate to create a new post under our "Techincal QA" board.