What are the requirements for transitioning from the 800k baht banked funds to the 65k baht monthly income visa method in Thailand?

Okay, let's sort this out,

going from banked money method (800K baht) to the monthly income method (transferring in 65K baht a month) is the hardest switch to make.

That's because you have to meet the seasoning requirements for the FULL year of the extension you're on where you used banked money <- meaning you need to LEAVE the 800K baht in the account for 3 months after the extension is granted and then you cannot let the balance go below 400K baht the rest of the year

AND AT THE SAME TIME

you need to bring in 65K baht a month each month every month for the previous 12 months before you apply for the next extension.

In essence you're meeting TWO different requirements, one for the extension you're on now using banked money and one for the next yearly extension you're going to apply for using monthly income

Your 800K has to be remaining for three months in your account after application and cannot be below 400K until your next year's application is approved and you got your next year's extension, those are the requirements for keeping your CURRENT extension valid, not for the next year's extension. They will check these when you are applying for a new extension.