You can also create several keyword libraries. So I have a keyword library called Nature within which I have top-level keywords such as Bird, Insect, etc. There are hierarchies below that so you might get Bird>Duck>Mallard. I have another keyword library called Places, below which I might have Bristol>Zoo. So if I exported an image of a Mallard taken at Bristol zoo, the keywords I would get in the export would be Bird, Duck, Mallard, Bristol, Zoo, but not Nature and not Places. Also if I chose not to export the Places keywords, I would just get Bird, Duck, Mallard.
Does that work for you?
Ian