You can always add a new domain name in cPanel as long as your hosting account allows it. It doesn’t matter if it’s registered with Brickellhost or somewhere else.
How to add a new domain name in cPanel?
1) Login into your Client Area
2) Click on your active hosting plan or the one to that you want to add a new domain name
3) Click on the cPanel button
4) Now look for the Domains section and click on "Domains" and click on it
5) Click on "Create new domain" and enter the domain that you would like to add
Note: The domain name must be first registered so you can add it. Otherwise, it will be rejected.