Is there any way to create a custom advanced alert, that knows when a server happens to go down due to a manual shutdown rather than just becomming unreachable?
Probably not because this alert would still have to rely on unsuccessful ICMP replies; which won't say anything but timeout. what you could do, with a little trade-off here is to increase the polling time frequency for the servers that are considered DEV, TEST, or shared servers. Granted the trade off is reaction time to down servers and OBTW gaps in response time charts for those nodes if the polling frequency is greater than 10 minutes and you have the chart time set to something less than that...
If you have your Alert Suppression Process documented and bought off on by management, then burn those developers at the stake and they should come around to following the process more frequently. Another random thought on this: If you have some snappy developers then get one of them to write a script to trigger a syslog message to you Orion server on a planned shutdown, and have it sent just before the server is down, then you could use that message to develop a useful/more viable automated alert supression... just a thought
and welcome to the forum