Hi Marc,
It should really work via the menu if you use the Remove Overrides option, otherwise there may be a character format you do not know about (possibly applied via the EDD ?). If you cannot remove the overrides this way, it may not be possible to remove them by a script either.
I do understand you want to do it range by range, though. Are you going to remove all character formats from the paragraphs or just remove the overrides while keeping the character formats that were applied?
Ciao
Jang