I assume they are talking about the splash guard / aeroplate underneath the engine which helps with MPGs to some extent. The plastic engine cover doesn't even need to be touched during an oil change.
Look up the plastic clip part numbers on a Honda parts site, then cross-reference them via eBay or Amazon to get a significantly cheaper knock-off. I've been able to get a bag of 20 for the price of 1 bought from the dealer parts counter. If they don't last, well you have plenty of spares now.