How to change url of “adverts” category?

Hi Greg,
thank you very much for your support.

I tried to add the code in my functions.php and the name of url are changed! But… unfortunatly when I click on the “new” url I find 404 error “page not found”.
While, if I try to show page’s categories or the classified I show correctly the web page.

So, when I add the code the url changing but if I try to click on new url:

www mysite com/classified/opel-zafira/ –> page not found 404
www mysite com/ad-category/cars/ –> page not found 404

www mysite com/advert/opel-zafira/ –> work, ok!
www mysite com/advert-category/cars/ –> work, ok!

Where I was wrong?

Thanks a lot!