I think this may be one case where there is a difference between mac and pc users. I'm pretty sure that iTunes stores song data in a xml database in (or adjacent to) your your iTunes music folder. Honestly, I'm not that great yet - my understanding is limited to using the tools that others create. I'm learning slowly though. If you figure out what the deal is with the apple lossless codec''s support for tags, let me know - I've been puzzling on that for almost a week now.
Here are a couple of links that will give you access to people with lots of knowledge:
Apple Support Forums has some really advanced cats. There are likely people there who can help, even if you are willing to dig into programming.
If you're using a mac, check out
Doug's AppleScripts for iTunes. With 386 scripts already written, you can probably find something that will help you.
Also for mac users - it has recently become clear that iTunes uses "hidden" tags to manipulate the behavior of some tracks, while not yet providing access to the user. These include episode and season information for TV shows.
Lostify will give you access to these hidden tags (at least the TV show ones). Even if you aren't a mac user, some of the info on that site might start you out towards programming your own data manipulation tools.