Multiple sets of ID3 GEOB tags with the same key

[Christilut]

I have files that contain the same GEOB key twice. It's not a valid header because of that but I do have to work with it. Mutagen seems to read the last set of these GEOBs, whereas the software I have to work with reads the first set of GEOBs.
Here is an example in kid3:

I would like to fork mutagen and change this particular behavior so mutagen reads the first set of GEOBs instead of the last. Can someone give me a pointer where I would have to change this? I'm not familiar with the code and not really a Python guy so I'd love to know where to start.

Thanks