Surely the initial 90 day non O is just a visa to stay long term? The 800k would only be needed at the time of applying for the one year extension based on retirement?
So you need to print off the appointment email to prove you have an appointment? Don’t they have an appointment system or is that too sensible, too non-Thai?
Yes do it that way. Get a 60 day tourist visa, which you can extend for 30 more days. Get a condo rental for 3 months and take the contract with your passport and as much Thai baht with you as possible to the bank. Show those documents and the cash to deposit and shouldn’t be a problem to open.
It’s how they ‘word’ it. They don’t charge a fee for the activity of changing the ticket information BUT they charge for any difference in fare between the 2 dates.