As well as changing your /etc/hosts as advised above, if you want CRA to know about the new host name, the HOST env var should give you what you want.

E.g. (this can go into your package.json under scripts/start)

HOST=somedomain.com react-scripts start
That should start your CRA-based dev server, listening at that domain name, and it should open/refresh a browser tab pointing there.

Edit: docs on this and other env vars that CRA uses.