Hi ArtZ! This is a really good question and some interesting solution too! 💡
In the past and at the present moment, we haven't had a direct way to replace icons with a newer version. At the moment, it is only possible to add new icons and remove old ones within an icon set. This article explains it: https://support.iconfinder.com/en/articles/18150-how-to-add-to-or-delete-icons-from-an-icon-set
As Laura said, there is a loss of the icon's rank when this is done. The old icon that is deleted had earned a position in the search results through the downloads over time. The new icon starts from scratch.
We see the need for a replacement feature more and more. First, because there are icons that are faulty and we ask the designers to fix them. Second, because improved versions of the same icon are welcome and very important to keep the content up to date. And we might just use Github to handle the file versions, as you suggested!
I have just added this to our list of feature requests and shared it with the team. I cannot promise a specific date when we will have this, but it is on the roadmap. Thank you so much for sharing! 💗