Add multiple aliases referring to a single node

I'm trying to add a custom link in my sitemap.xml

In my site I have the node/176 that has 4 aliases (for SEO optimizations) but if I try to add the aliases as custom links I have the error
"There is already an existing link in the sitemap with the path node/176."

So what's the utility of adding a custom link if I can't add a custom alias?