You can replace store_closed.html in the root of your store with anything you want. But do note that it may be overwritten upon upgrade so you should have a way to quickly restore your customization. You won't be able to add a registration form unless you provide a handler for the Exception that will allow you to submit the form (or go through the registration process) before returning to the store_closed page.
How I can make another page root because I want send email form
You can replace store_closed.html in the root of your store with anything you want. But do note that it may be overwritten upon upgrade so you should have a way to quickly restore your customization. You won't be able to add a registration form unless you provide a handler for the Exception that will allow you to submit the form (or go through the registration process) before returning to the store_closed page.
Sure it's possible. Any developer can do that for you. But I'm assuming you are going to want to track those specific emails and when the store opens, automatically notify them and remove them from the list.