Create Your Own Holiday Calendar From A Subscribed Holiday Calendar
Use this tip to delete any events from a Subscribed Holiday Calendar
1. Use Calendar>File>Export>Export...to save a copy of the US Holidays Calendar on the Desktop.
2. Uncheck the US Holidays Calendar in Calendar>Preferences...>Show Holidays Calendar.
3. Double-click the copy which was saved on the Desktop and import it as a "New Calendar."
4. Delete events as desired.