You don't need to change a Visa if you have a non-O based on marriage you can go straight and apply for a work permit no need to change visa no need to go to immigration. Extend your non-O or get the relative documents and change it to a Non B at immigration when you go to get your extension. Your allowed to get a work permit on a Non O based on marriage. Some employment offices just see a Nom O a flat out give you a work permit even on a Non O Marriage. (Chonburi & Knon Kaen) offices. Though this should not of been the case.