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@Steve ******
correctly stated IF you're on an extension based on employment you don't need ANY Non-O VISA.. All you're doing is changing the reason for your extension from employment to marriage
You'd go to the immigration office cancel your employment extension and immediately apply for a new yearly extension based on marriage by meeting the documentation and the financial requirements for 1900baht
You'll get a 30 day under consideration stamp and then after a month go back and get the year extension inked in.