You can change the DNS PTR (reverse or ) record of any of your IP address, by simply click on that IP address from your Hypanel account. You can access Hypanel from here: https://panel.intovps.com
This is no longer possible from Hypanel for OpenVZ.
Just ask support to do it for you if you still have an OpenVZ VPS.
For OpenStack you can change it from Fleio directly.