Windows uses backslashes nativelly, so players copying the path right from Explorer will have to add extra slashes or change all the slashes. That is to be explained to users. Hope, there are few users who have a separate collection.
There is a possible workaround - use forge.util.FileSection.parse(Iterable<String>, String) to parse the properties file. It will treat lines literally. The only improvement to be made about that method is support of comments.
Picture collection... I don't want the collection automatically renamed or anything like that. There was a request for custom paths to picture collection
viewtopic.php?f=26&t=9467, and I was one of those who refused to intergate it. Now looks like we I got in a situation of the one who needs customizable paths to sets.
So, I'll tell you what this will look like. Another option in preferences file, which would hold a map serialized in a single line. That map will be keyed by set code and it's value is the subfolder of cardPicsDir for that certain set.