Question on freezing meals
When making suggestions regarding the freezing of foods, it is assumed that the food has been handled properly and stored at proper temperatures for no more than a period of time during which it remains safe to consume. It is also assumed that the OP seeking information has a quality freezer that can maintain a proper temperature for storing frozen foods. Before making any decision concerning the appropriateness of freezing foods, cooked or raw, always review USDA food safety recommendations for the product under consideration.
Herbs like basil, oregano, tarragon tend to hold their flavor when fresh frozen. Others; not so well. Spices are less of an issue. Depending on the herb you've selected, you may find that your plan will work just fine. Inasmuch as you've already blended them into a rub/crust I assume they're mixed into an oil (e.g. olive oil). If that's the case they'll freeze better.
I would strongly recommend vacuum packaging your crusted duck breasts before freezing to reduce any flavor losses you might otherwise experience.
And do NOT, I repeat, NOT store in the freezer section of a freezer for more than a few days. It may be ok, it may freezer burn or sit in a "hot spot" and partially thaw/refreeze repeatedly. Best not to take the chance with something like this. If I had my druthers I'd have a fridge with an ice box only (just big enough for making ice cubes basically) and everything else would go into a deep freeze. Even popsicles, LOL!
If its not going to be removed and consumed in a few days, a fridge freezer is no place for good food.