Does changing one's madhhab from Sunni to another affect the validity of the marriage contract, especially with doubt regarding the time of the change?

The educated Muslim who can discern the closest schools of thought to the Sunnah should follow the evidence and prophetic guidance, seeking assistance from the words of scholars in understanding the authenticity and implications of the evidence, and benefiting from the preferred opinions of scholars who preceded him, without limiting himself to his own understanding. Adhering to a specific madhhab is not obligatory, and it is permissible to move between madhhabs. This does not affect marital infallibility.