pre-book course in restaurant reservation

Hi! One more question. When I make online reservation for restaurants in Japan, it asks whether I want to select a course (the restaurant has both course menu and a la carte). If I haven't decided, can I choose not booking at this time (指定なし）, and still order a course in the restaurant? Or if I don't choose it during reservation, I miss the opportunity to do so once I'm there?

Thanks again!

Depends on the restaurant. Some fine dining restaurants need confirmation in advance to plan/prepare the ingredients, especially if the items offered in the set menu are different to the ala carte menu. Hence, a lot of restaurants charge cancellation fees, eg 50% 3 days before, 100% on the day

Some restaurants such as yakiniku will allow you to order set or ala carte on the day because they only need to slice/cut various meat parts

Thank you! If I don't have to pay in advance for the reservation, does it mean that I probably can still order the course once I'm there then? Or it's really case by case so I should just call the restaurant (and use my broken Japanese -_-b)

It depend on the restaurants. Some restaurants requires advance order for the courses, and cannot order courses on the day of the reservation. Some restaurants limit the courses customers can order on the day of the reservation.
You can make requests for reservation from following site: https://autoreserve.com/en/
From this site, you can choose the course in advance when the restaurant requires it. Happy travel!

For smaller restaurants or those serving fresh items (like sushi) they may be buying for a course meal on the day and need to know in advance.