My system (F22) started developing problems and I finally had to reboot. I run the script a number of times and strangeness was occuring, ending with /dev/sdb not disapearing after removing one mSD card, and then could no longer dd to new cards that were trying to mount as /dev/sdb. I don't know if the script was at fault or something, else. But things definitely went south.
Just wanted to clarify, did you try to run the changeuuid.py script on the same card as the one running the OS?
One clear problem with this script is that the [INFO] messages report the old UUID wrong after the first time run. Each time it lists the old UUIDs as the last UUIDs. Not the UUIDs on the device.
The output of the changeuuid.py script would be really useful in debugging.