@Jack ***************
you need to understand, you can surely empty you account after you have been granted an Extension of Stay Permit for one year.
However, the one year extended stay permit requires you to show the 400,000 THB back in your account two months before you apply for the next Extension.
Because you current Extension is based on the deposit method, you will need the 400,000 THB on your account until the very last day of the expiry of your current stay permit.
After your application, Immigration allows you to use the income method and will issue a new Extension based on marriage using the income method.
Only AFTER you have been issued the new Extension, you can clear the 400K from your account
Not any sooner than that! Don’t easily trust what people tell you. Always expect the unexpected – and this includes the Thai Immigration