Where is the custom config saved on the system ?
On the CP:
If you need to access the location of custom config file on the Control Panel you will find it here:
On the current HV:
Cloud Booted Hypervisors load their root filesystem from an NFS share on the control panel.
Since Cloudboot HVs are always booted from a standard image, they lose any custom changes which are made anytime they are rebooted.