Can I Exchange Foreign Currency to Thai Baht After Getting a Non-O Visa Based on Retirement?

Remember IF you are using banked money (baht or foreign currency) for the extension of stay you need the 800K baht (or the equivalent) IN the account for two months before you apply for the yearly extension, it needs to STAY in that account for 3 months AFTER you get the extension and then the balance on that account can NOT go below 400K baht for the rest of the year.

SO I'd say NO you can't move the money into Baht after you got the extension because it'd move it out of that account, BUT that is my guess.

You need to talk to YOUR immigration office long before you need to apply for this extension to see what they will accept