@BetterRed: Have you looked at the Open With plugin? You should be able to configure an entry to open your executable against the file you want to change in the list. Maybe you will need to wrap it in a batch file to parse the folder path out.
I think what you are planning to do is from the directory path, read the metadata.opf file in the directory, determine the name of the RTF or PDF file and then execute a command on that file using the data from the metadata.opf. If so, I think calling a batch file with Open With get you were you want to be.
If that doesn't work, you can look at the plugins code to see how it gets the paths.