Are you talking about something like a hosting control panel? I don't have that, I own my own servers so have direct access via ssh and of course, browser.
Yes.
If you are using Apache then in your vhost file you have a line
ServerName mydomain.comAdd
ServerName mydomain.com
ServerAlias *.mydomain.comYou would also need DNS set up for either wildcard subdomains or a record for each subdomain that you set up.