pulling text from db to add to error message

What I would love to be able to do is run a Groovy script on alerts between the Alert Rules and Escalation stages of alert processing so that the alert message can be enriched or additional custom logic can be used to determine if the alert should proceed to Escalation stage (the script could return a true or false to control whether the alert processing continues normally or is aborted). 

Example use case, alert is triggered > alert rule is matched > script checks CMDB and change management calendar, returns false if CI is in change or true to continue to Escalation.