Getting output of alerts (like source IP) - not possible. You could use task escalate, but that would be difficult (although possible).
For general watchlist updating:
You need to use the OS and db scripts to do this. There is a batch file included with enVision ( I think) that can update it. There is also a powershell that can perform the same thing.
It will take the contents of a file and import it into a watchlist (overwriting it)
I'm looking for the ps1 script now. -> http://rsaenvision.lithium.com/t5/Tools-and-Scripts/dbUpdate-watchlist-cmd-replacement/m-p/2339