This cannot be done through WHM using the option “Change Site’s IP Address”, an addon domain wont be showing there in list since it is not as a seperate cPanel account. For to assign dedicated IP for addon domain, you need to follow up the below steps manually.
(Before all domains TTL value should be reduced to 300 and assign IP only after 4 hours to reduce the downtime)
* Goto /var/cpanel/userdata/username/addondomaname
* change IP(dedicated) there.
* Then go to addon domains zone file – /var/named/addondomain.db
* change IP there too
* Then do distiller command to update apache configuration — /usr/local/cpanel/bin/apache_conf_distiller –update
( Please vi /usr/local/apache/conf/httpd.conf and make sure the change made in effect in the addon domains virtual host entry, look the IP there if changed to new one. If not please take the backup of conf first and do change to new IP there in the addon domain’s vhost entry)
* Restart apache
After this you can install ssl for addon domain