How do I configure NPM to make node status to go to down when disk usage hits 95% - how do i do it?
First off, why would you want to do that? The node is not down at its most basic level (ICMP) just because a volume is full. If you are looking to track availability as it relates to volume usage, you could just run a report against the volumes(s) on the node and display how long they were over the threshold for a particular time period.
It might be possible by a custom sql alert definition, where in which you have to update the DB directly. But then I don't think that's a great idea as it would affect multiple things in your environment (in short the next NPM polling cycle would find out the node is up and it would change the status back to UP)