It wasn't supported until now. Pick up the latest source code. You'll be able to do
worksheet.ConditionalFormats.RemoveAll(); // Remove all conditional formats on the ws
worksheet.ConditionalFormats.Remove( cf => cf.Range.Contains("A1") ); // Specify a predicate to match which conditional formats to remove.
worksheet.ConditionalFormats.RemoveAll(); // Remove all conditional formats on the ws
worksheet.ConditionalFormats.Remove( cf => cf.Range.Contains("A1") ); // Specify a predicate to match which conditional formats to remove.