I am running Plesk on Linode (CentOS) and did setup main account as Linode's domain to access admin panel.
Can I delete it and still access login page to panel through IP addresses directly, or will it break something?
You'll have a beter experience accessing Plesk trough the host/domain instead of the IP address because of the SSL error. However I don't think it's less secure to access Plesk on your server IP.