Copying a customised theme to build from, in Builder

Hi there!

I hope you guys are great!

I've only now stumbled upon the magic that is Upfront Builder. But I'm afraid I have started from the wrong end. I'm already half way through creating a site based on the theme Panino. But when I go to edit it in Builder it of course started editing the original Panino theme. Is there anyway to continue working on my site in Builder but from where I am now so that I do not have to start over?

I tried searching for this, but could not find anything. Sorry if this is already documented.

Many thanks, Tom