Editing Goran Style Sheet

Hello,

I wish to use Goran on a new project and I know it is a child theme of Edin.

I want to make various changes to the Goran theme via the style.css and potentially the header.php file. How do I go about this without losing any amends once the Goran theme is updated down the line?

I cannot create a child theme of Goran as the “goran” theme is not a valid parent theme.

Any advice would be greatly appreciated.