The available options on escalation are : reassign, change priority, send alert and send message.
I cannot see an option to execute a script in the same process model.
is the only way creating a different process (and send message) ?
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You can have a 'Receive Message' start node in the same process model and use the 'Send Message' option in the Escalation to trigger that thread, at which point you can get it to do anything that is available to you in a process model. I recommend that you carefully document this in the process model so that it is apparent how this works and what it is doing.
This was my initial thought, unfortunately this is not working, see my thread:
community.appian.com/.../targeted-message-activates-another-receiver