The option to export as XML that can be pushed to the NSX API only works when you're grouping by Security Group. That said, if you've already got NSX deployed, you can pre-build security groups there rather than building applications in vRNI and export the rules that way.
I've been working with VMWare support which gave me examples of how to do every piece of the process using REST api. Security Tags, Security Groups, Firewall rules, etc.
This isn't a nimble process.
Thank you for the reply.
Please be aware that unfortunately VMWare is not able to provide scripts or script debugging support. VMWare can guide to documentation and any examples provided within documentation, however it is not able to help script the actual input/output that may be required for a given environment. This would need to be trial and error tested outside the realm of VMWare support. API scripting would also fall under this umbrella. The vRNI API does provide examples of things and how this output may be gathered from vRNI through API, however the support of automating this API output, and then input into NSX would not be supported.