Is a wife forbidden to her husband if he said to her: "You are forbidden to me if I had done such and such," and she did that, and what is the legal way out, considering the fatwa of one of the authorized marriage officiants to feed ten needy people and not inform the husband?

The gist of the matter is that your husband has made your prohibition conditional on you doing a specific thing. If you do it, what he intended will occur. The preponderant opinion among jurists is that it refers to the husband's intention regarding this prohibition: is it ẓihār (a form of divorce), or ṭalāq (divorce), or an oath? Therefore, you must refer back to your husband to ascertain his intention. If he intended it as an oath, it is not permissible for you to offer an expiation for an oath on his behalf except with his permission.