Follow the below steps to assign a dedicated IP to either a parked/addon domain in case of cpanel servers.
Edit DNS zone of addon to point it to the new IP and also change the subdomain IP to that same IP. This can be done from WHM.
Edit the file /var/cpanel/userdata/username/subdomain.domain.com file, change the IP and save it.
# service httpsd restart
Login to WHM and generate a CSR from the ” Generate a SSL Certificate and Signing Request” link.
After you have the certificate, click on the “Install a SSL Certificate and Setup the Domain” link and paste the crt into the top box.
When you tab or click off of the text box WHM will auto fill the other values and I was surprised to find it used the correct IP address and username right off. So just verify the values are correct and then click submit.