I just tried overriding the canCloseIncident function from the IncidentUtils script include on my Personal Dev instance and it worked. So anyone with an itil role will be able to see the 'Close Incident' UI action and click on it to close the inciden...

Wouldn't it be simpler to change 'itil_admin' to 'itil' in the Script Include global.IncidentUtilsSNC?

In response to Sergio's post above, wouldn't it be simpler to change 'itil_admin' to 'itil' in the Script Include global.IncidentUtilsSNC