It is currently impossible to edit the URL of a Knowledge Base category in HubSpot.
At the moment, the URL of the category automatically matches the name of the category. We should be able to edit the URL of a category, as we are able to edit the URLs of the articles.
This is a needed feature, as it would allow for example to be able to delete accents in the URL but keeping them into the category name.
I would like this as well. We always adjust our url to our categories (knowledge base/category/article) but because the categories themselves are not changable, their URL is different from that. Category names are sometimes long so the URL also becomes rather long, which might be bad for SEO as well.