You cannot use the same domain name for two different Webflow projects. If you’re looking to create a completely different site, but on the same domain name, why not try using sub-domains instead.
We do this, at Webflow, for our sites. Examples:
https://interactions.webflow.com/
To do this, just setup a CNAME for your subdomain, then add that full domain to your custom domain names list of your site.
Hope this helps 