Not sure how you are going to pull that off but here is code for adding users to a list field that relates to the sys_user table. Adding or removing an Affected CI in the related list will trigger an update of the List field and add assigned to from all the related CI's to the u_service_owner field.
List field on Incident table called u_service_owner referencing sys_user table.
Business rule on task_ci table. Runs after on Insert, Update and Delete.
Script:
(function executeRule(current, previous /*null when async*/) {
// Add your code here
var inc = new GlideRecord('incident');
inc.addQuery('sys_id',current.task);
inc.query();
if(inc.next()){
inc.u_service_owner=''; //Clear service owner list
var ci = new GlideRecord('task_ci');
ci.addQuery('task',current.task);
ci.query();
while (ci.next()){
inc.u_service_owner += ',' + ci.ci_item.assigned_to; //Add CI assigned to
}
inc.update();
}
})(current, previous);
