i used x10 subdomain as my main domain then i wanted it changed to my own domain and some of the staff changed it
that was long time ago, idk if it can be done now
There is an option in cpanel (packdomains) that allows you to place different domain that has registered (x10 propocionado different from the default), domain server free or paid ....
consider that perhaps they will have to modify the source code of the web ....