I have seen Yahoo add a site to a topical category and a regional category upon submission. In other words, say you sell home made cookies on a national scale but you also have a local store. You could get listed in a national cookie type of category as well as a regional one related to your physical location. These are the kind of scenarios where I have seen Yahoo list a site in two categories. And many times, Yahoo did it on their own without suggestion from the submitter.
However, I believe Jill is correct in that you can't pay to be listed in a 2nd category. You can submit alright, but they'll just keep your money and tell you "Sorry, Charlie! You're already listed.

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If you are already listed in a national type of a category, put in a Change Request and ask to also be listed in a regional category, if it is applicable that you be listed there (i.e. you have physical location there, corporate headquarters, etc.).