How can I create a custom site deployment (production-test)?

Our use case is:

We have one repo on github and we want to have 2 diffrent site deployments on that repo for production - e.g. different URL, different env vars (defined in a netlify.toml in our project) etc.

I couldn’t find a way to do it - looks like there are reserved:
context.production, context.staging

Can we customize this? we need to have a production-test site.

Thanks!

If all you need is to change env vars, why not just add the env vars in Netlify UI? Are you looking for something else too?