Edit Some Code in My Newspaper Theme

Hello i want to add some additional feature in my newspaper 9 theme , it is not related to design , i want a script to be added in theme , like if someone with special value in the url visit my website , they will be loaded again and this time that special value will be removed from their url and some hidden button will get visible to that url , if someone with no special value visit url , they will visit the website normally and hidden button will be not visible. and that button will redirect user to a url that will be based on the special value. visit this url [login to view URL] just like this.