SEF url options

Hi,

It's not possible to remove both. Otherwise, when routing the URLs the system doesn't know if it needs to look for a product or a category based on the alias in the URL.
If you really want to have whatever URL you want regardless of the restrictions in place by how the routing is done in Joomla / HikaShop, the only solution is to use a SEF extension. I would recommend 4SEF:
extensions.joomla.org/extension/4sef/
The way it works is that it keeps the non-SEF and SEF URLs in the database when the SEF URL is generated from the original non SEF URL. That way, when it routes the URLs (someone clicks on a SEF URL and it needs to provide back the non SEF URL for it), it just have to query the database to get it.