Lauri tagged Mike which is a Geni employee to get his attention to your request.
I don't think Mike can help on this - gedtweak was developed by a Geni user and have not been maintained since the initial release for 3 years ago.
Every time I have tested gedtweak it failed downloading more than a few images.
Have you tried to load your GEDCOM from Geni directly into gramps?
The photos are tagged as URL's in the GEDCOM and several programs have showed that they are able to download the photos directly from Geni, but a program like gedtweak would be a nice program to make a complete backup of your Geni data by downloading all external elements as well.
You can just hope that someone develops a similar program.
I got a patch from the gramps development team to import my geni data to gramps. This is working fine now. But I see no possibility to convert the links from the photos within gramps so far.
I could download about 90 photos with gedtweak. But as mentioned before my GEDCOM export file with the adjusted links got corrupted.
Have a nice day,