What is the ruling regarding a husband saying to his wife: "You are unlawful to me if you do such and such," and then the wife does it more than once?

What your husband uttered is a suspension of your being forbidden to him contingent on the specific act he intended. The preponderant view is that the forbidding of a wife depends on the intention of the one who utters it. If he intended ẓihār, it is ẓihār. If he intended divorce, it is divorce. And if he intended an oath, it is an oath. Since you have performed the act upon which your husband suspended the forbidding, what he intended—whether divorce, ẓihār, or an oath—has come into effect.