This may be the most minor of bugs, but I notice that when this script is used on an image that uses a hierarchical keyword, the keyword in the new image (with the alternative format) has been moved to the root of the keywords list.
Eg. Photo uses keyword “Arts”, from “Photojournalism/ Arts”.
“Arts” does not exist in the root of the keywords list.
Following the format conversion, “Arts” can now be found in both the root of the Keyword hierarchy, and in its original location.
A smart album that had been set to search for “Photojournalism/ Arts” will now not include the converted image, as it's keyword is actually different.
There's a simple fix; I drag and drop “Arts” (in this example) back to it's hierarchy position, and it merges the two keywords.
Just thought I'd let you know.