Adobe Portfolio - Duplicate site

Apparently not, still. Seems like a no-brainer feature to me and pretty annoying they haven't added this yet.

at the bottom left of your portfolio edit page you can use preview and not use update live site:

<moved from download&install>

Portfolio as far as I know has no testing/staging environment, nor does it have that as an addon option. If you need a more complex website that does this, you might need to look to move your site off Adobe portfolio.