@Giggiux Not sure what you mean. If you move a topic from one category to another, it disappears from the first category. I was suggesting the capability to have the same topic listed under multiple categories.
Meta keywords aren't really relevant anymore. It's a "nice to have". If you have it it's great, because Google isn't the only search engine in the world. But it absolutely does not impact negatively on SEO, unless you're padding it with unnecessary unrelated content, which is what Google wants to stamp out.