I've been thinking about this a lot and just did some experiments. I think Genre will definitely work for this for sure. But it seems a little clumsy to me because, while Genre is a list type, it's edit type is Standard. Which means you can't select genre from a multi-check list in the Tagging Pane like you can with other List type fields, which have their edit type set to List. You can choose from a check box list in a Pane, but then you can only choose ONE value! To enter documentary as a second Genre (say Comedy and Documentary), you have to use the semi-colon style and enter it manually: Comedy;Documentary . Clumsy for editing if you're going to be doing it often, or selectively, as opposed to just a couple of large batches.
I think a few other methods bear consideration:
1. Super Genre: Make a new field called [Super Genre] where you put these types of things. Documentary, Kids, etc, could all be a Super Genre, and retain the regular Genre tag. You could easily build views based upon the value of Super Genre or a lack of value of Super Genre. In some cases it might make a lot of sense to just match on [Super Genre]="" (empty) and only show items that have no Super Genre set.
2. Keywords. Keywords are a list type, with list editing. It would be very easy to edit using keywords because you could click a check box to select Documentary (or Kids, etc). Again, views could easily reference Keywords. You would have to specifically provide the keywords you want to exclude though: -[Keywords]=Documentary -[Keywords]=Kids .
3. How about just a field called "Exceptions". Fill in Exceptions with anything you want, and build your views to (normally) ignore anything that has Exceptions set. Again, Exceptions could be Documentary, Kids, News, or anything else you don't want in your "normal everyday" views.
I lean towards #1 above (Super Genre) because it seems to make the most sense in terms of classification. But I can see doing any of these methods and having success. All of these are easier to edit because you have either multi-checkbox fields, or new fields that you can easily edit using checkboxes. Both easier than editing Genre with more than one value.
This is another one of those personal preference things. I'm just sharing my ideas.
Brian.