Will closing my bank account to upgrade my fixed term deposit affect my Non Immigrant O (Retirement) visa extension?

I did this exact thing about 3 years ago. Kept both books together and was no problem at renewal.

I have been in Thailand for about 18 years, with about 10 of those on retirement Non O extensions. I brought over my 800,000 way way back when, and have moved the money into new accounts again and again. I have never ever had an issue with immigration regarding this, all they seem to care about each time is the bank letter....and what I find amusing is that the last time I got the bank letter, I actually went and translated it, and all it says is that I am the owner of this account, nothing as to where the funds came from or when, it's as generic a letter as the embassy letters "verifying" residency or income used to be. That said, I ALWAYS bring the previous bank books (1 or 2) to show immigration that I opened a new account with better interest or that the previous CD had expired, and I also have gotten printouts from the bank going back xx years to show that I did indeed move the initial money from overseas. Have never had to use them, but am prepared.

In the past 2 years I have closed the same Bangkok bank orange book account to access the higher interest rate twice and when renewed O visa in Feb at Jomtien no problem at all.

Do you still have immediate access to the cash if you wanted to withdraw?

Good question,

I'd say IF the money never leaves the bank and one account is closed and the new account is opened right at the same time you'd be okay. BUT that's just a guess.