What is the ruling on switching from one madhhab to another after having acted upon the first, such as divorcing a menstruating woman out of ignorance, then later learning of Ibn Taymiyyah's opinion?

Whoever is not among the people of ijtihad (independent reasoning), must ask the people of knowledge and act upon their sayings; based on the words of Allah the Almighty: "So ask the people of the Reminder if you do not know," and based on the words of the Prophet, peace and blessings be upon him: "They killed him, may Allah kill them! Why did they not ask when they did not know? Indeed, the cure for ignorance is asking." As for retracting from following one madhhab (school of thought) to another, even after acting upon it, this is a matter of dispute.