How about this option: nfs.export.auto-update
The manual page for options describes it so ...
The default for this option is enabled. This option controls whether automatic updates are performed on the /etc/exports file. If it is not set, then the commands vol create, vol delete, and vol rename will not automatically rewrite the file. Instead they will syslog the need to edit the file. When volumes are moved between vfilers, automatic updates on the /etc/exports file of the source and destination vfilers are dependent on this option.
Robert Watson is right.
Every volume created will automatically have an NFS export created for it. This means that if you’ve exposed NFS functionality to your IP network, your volumes will be presented via NFS to anyone on your network. The default permission settings aren’t (fortunately) blown COMPLETELY open, but they are not locked down, and frankly, the export should not be created automatically. You’re already creating the volume, it’s not difficult to take it one step further and create the corresponding NFS export, in my opinion. In technical precision, this option will control whether or not volume-related commands make changes to the /etc/exports file.
options nfs.export.auto-update off