Hi,
Yes, it needs developer skills to do that.
To develop a plugin similar to what is in the Google Products plugin but for the specs at
developer.skroutz.gr/feedspec/
will require a confirmed developer to spend at least a few days working on that.
So that's not cheap. It will cost several hundred euros, maybe a thousand or more.
If you're a developer, you could look at the code of the Google Products plugin, make a new plugin based on that code and modify the plugin code to adapt it for these specifications. You can find the code of the Google Products in the plugins/hikashop/google_products/ folder.
Note however that if you have a lot of products, and your hosting doesn't want to increase the resource restrictions on your website, and you don't want to change your hosting, you'll end up with similar issues with your new plugin...