If you are left-handed, you may wonder if there’s ever a time when playing right-handed is preferable?

In my opinion, this would only be the case in a very formal performance situation. In a classical orchestra for example, it would be a little awkward if one of the violin bows moved in the opposite direction poking someone in the eye!

But unless you are planning to play shamisen in a such a formal ensemble, (and if the formal ensemble is that conservative, simply being a foreigner might be a deal-breaker) there is absolutely no reason to use a hand that feels less natural for you.