Managing the redirects caused by post name changes

In my blog I have all articles permalink to a TOPCATEGORY/TITLE, like example.com/bar/raising-the

I also have many subcategories, so for example the category “bar > bar stools” is at
example.com/bar/stools

This obviously has some conflict potential, but I believed the gains of having a clear navigations outweight potential conflicts which could be resolved later.

I found my first conflict when I wanted to create a category (“foo”) that was already used by a post permalink. So I went and edited that specific post permalink to some other word (“cooking-with-foo”) so I could still have the very good url of
example.com/cooking/foo
reserved for the category.

The problem now is that wordpress has a default behavior of keeping the old permalink of that post reserved, so I can’t create the category link I want. I understand this behavior and it’s usually good, since it keeps old redirections. For example, now
example.com/bar/foo redirects to example.com/bar/cooking-with-foo

How can I resolve this? I’m willing to edit the database manually, but I am just afraid that this might break something