How to code custom special page

Because you asked “How to Code”, here is my guide to get you started.

1. Create a menu page in the administration area using add_menu_page
2. Create the form using html select form-element
3. Populate the form-element with all pages. To get all pages you can use get_posts()
4. Save the form using admin_post action
5. Save the selected-item of the form using update_option()
6. To get the saved option you can use get_option()
7. To add that — Special Text in the page list, you need to filter the title. If the page’s ID is equal to the saved_setting, then append that text. I’m not sure which hook to use, I think it is manage_pages_columns

I hope it helps.