Just for info please see below a copy / paste of the advice I received:
"
To clarify, in order to renew your Marriage Visa, Thai immigration requires that a minimum balance of 400,000 THB be maintained in your Thai bank account for at least three months after the initial extension of your Non-Immigrant O visa to a one-year Marriage Visa.
Throughout the year, you may withdraw funds from your account; however, the balance must not fall below 200,000 THB at any point. Then, two months prior to your next visa renewal, the account must once again reflect a minimum balance of 400,000 THB.
Based on this requirement, even if you top up your account with 400,000 THB now, you would not meet the financial criteria for the past year. In this case, the only available option is to leave the country and apply for a new Non-Immigrant O visa, thereby starting the Marriage Visa process again.
"