I keep the 800k in a dedicated account (term account...usually for 10-13 months per term) at Siam Commercial Bank and that passbook cannot be updated regardless of whether I or a bank teller sticks the passbook in the machine. When I obtained the new-one year extension a few months back, I simply presented the bank letter and a copy of the passbook (which showed that the current term began in December of 2018) and there was no question or issue about any updating.
However, from what I gather from some posts, some people have claimed that they've been required to update the passbook the day of application and I believe that most or all of these involve people who have kept their 800k in a regular savings account that is able to be updated (and able to be altered by small deposit or withdrawal) on the day of application. If posters have personal experience with this issue at CM Immigration (please don't post here about Nakorn Nowhere), please advise.
I'd also note that based on recent experiences of friends, you really don't need to get to Immigration early any more. Some....even for annual extensions....have gone in the early afternoon and been out of there in less than an hour. I arrived for my annual extension at 11:05 and was finished (including a new re-entry permit) at 12:25PM....not too shabby.
Based on some reports, you might want to avoid going out there on the day before or after a Thai holiday (one where Immigration is closed) as the office could be very busy.