I have a live site with an existing web host; the domain is reg'd with an independent third party. I would like to sign up with a different host, but this host requires me to provide a domain for the new site. I'd like to use the existing domain, but I don't want any changes to DNS or downtime on the existing site, while I build the replacement at the new host. Why is the new host requiring a domain? They offer a temporary URL / IP-based access for new sign-ups, so I don't understand why, strictly speaking, a domain name is needed for sign-up.
( This -- If I use a web hosting service with a custom domain name then later want to move to a different host, will I be able to use that same domain name? -- was the closest thing I could find, but doesn't really answer my question ).