Thanks all, makes things a lot clearer

So when I duplicate a product and change this it would not work.
As Jörgen said sound kind of workable but i'm not sure how this is done...in media can I duplicate a file??
This a kind of wonky, but if You create a image media with a filename that exists You will get a new media item.
This item gets an extra extension added f.e _typeless
If You then add your image url to the media item, you will actually get two media items that point to the same image

In other words only one image stored on the disk, but two media items.
Thanks,
Pas