The right side of the Incidents screen has a link to an Incidents Overview workbook that I would like to customize but I can't find it in the list of Workbooks templates or My Workbooks. Where is this kept? are we prohibited from editing it?
You can EDIT it. When you open it in Edit mode - its actually tells you that (see picture). I often replace the content with "Investigation Insights" workbook - just make sure you SAVE, Incident Overview from the templates blade first (and take a copy in case you need to roll it back), it will still be called "Incident Overview" but will run whatever you like.