If I’m understanding you correctly, you’re looking to just show a specific set of posts on a page? Usually you’d create a custom template with your custom query on it instead of using a default template in WP.
As far as switching something based on something used in the admin screen, I’ve used Advanced Custom Fields plugin for adding an option to a post screen, then filtering my WP query (in my custom template) based on that option at the time the page is rendered.