How do edit the default zone file

Hello, I would very much like to edit the default cPanel zone file created for new accounts. At present, the MX record for new accounts is set to "example.com" I would prefer this zone to be created as "mail.example.com" I would also prefer the "mail.example.com" to be set as an A record pointing to the IP address of my server. The default configuration has caused a number of mail delivery problems, specifically regarding WIX sites or any site hosted on another server.