Alarm generation and actions are different things. For generating alarm you do not need an action - it's just special attributes in event processing policy rule. To set rule to generate alarm, do the following (assuming you already have rule object called "rule" of type EventProcessingPolicyRule):

rule.setFlags(rule.getFlags() | EventProcessingPolicyRule.GENERATE_ALARM);
rule.setAlarmMessage("%m");  // it's an example, you can specify your real alarm message here
rule.setAlarmSeverity(0);   // specify your severity
rule.setAlarmKey("");   // specify alarm key

and to set rule to terminate alarm:

rule.setFlags(rule.getFlags() | EventProcessingPolicyRule.GENERATE_ALARM);
rule.setAlarmSeverity(Severity.UNMANAGED);   // Severity UNMANAGED indicates alarm termination rule
rule.setAlarmKey("");   // specify alarm key

Also, you can take a look at property pages in nxmc-epp plugin in management console.

Best regards,
Victor