Can a "Custom View" be stored to a custom default template and thus be made available to all Excel workbooks, new and old?
I think VBA is the way to go on this. You could consider going into the XML - I thought that custom views might be defined as a separate XML file in the XLSX archive. But it's just a <customWorkbookViews> section in the xl\workbook.xml file. And you could maybe do it with a template, depending on how your application works. But honestly, the simplest thing is probably just to record a VBA macro in the Personal Macro Workbook (so it's always available) and add it to the Quick Access Toolbar. (Yes, I try to avoid VBA where possible, but here it's the best way.)