Our detectives are back with the following intel on this WordPress site
The site is using two themes, one child and one parent. The child theme is based on the parent and often custom to the site. The parent theme is Enfold theme by Kriesi .
We could identify 3 plugins (there might be more) - Cookie Notice for GDPR , Google XML Sitemaps and Yoast SEO
A Child Theme for the Enfold Wordpress Theme. If you plan to do a lot of file modifications we recommend to use this Theme instead of the original Theme. Updating wil be much easier then.