I wonder if this functionality is now available in the latest version of NCM.
The post marked as "correct answer" does not address the original request:
Only issue the write mem command on devices where the start-config does not match the run-config.
Here is my thought:
There is a report that shows run/start config conflicts.
Based on the output from that report (dynamic selection) run a script that issues the write mem command on only those devices.
Looking in NCM there is a Group by "last login result" in the drop-down for select nodes to run a script on.
If this could be enhanced to add "Config conflicts" then this would be a simple matter.