Can I transfer my bank account after moving locations without affecting my Non-O retirement visa extension?

There's no need to transfer banks.

I moved area and thought I needed to, but you don't and I have successfully extended for another year in my new area, using a different bank branch.

The bank provided everything I needed for the extension on the day.

As for the fees, if you use the cardless withdrawal method, no matter where you are in Thailand it is free ( I withdrew money today and it's really easy).

Open a new account, transfer 400+ but leaving 400+ then, when the first 400 is definitely received and in your passbook transfer the rest. Don't believe the close one before opening the other shite.

could indeed screw you up, and you could get around it by just opening an account at the branch in hua hin, and once it's already OPEN do the transfer.

OR

Seeing as you're using banked money method, AFTER you get your next extension and have left the 800K baht in the bank for 3 months, you can have the balance go to 400K, move HALF the money, keeping 400K in the Chiang Mai account and putting 400K in the Hua Hin account, and once you do that THEN you can move the rest because you will have kept the seasoning requirement of no less than 400k baht balance in an account