I do my extensions at CW.
I've also changed accounts at least 3 times already on this visa. Started with 800K equivalent in an FCA at SCB, then went over to a baht account at BBL. Now in baht with KBank.
Yes, both the savings account and the fixed deposit I'm discussing here are at the same bank, so I'm not changing banks again this time. Only accounts.
But the question was about spending out of one account immediately when you don't plan to use that account again for an extension the following year.
Thinking back now, I think I probably already did that once or twice in the past when I switched banks. I may have not started using the money in the account immediately, but in most cases, shortly after getting the visa extension stamp, I closed the account that would no longer be used for the next extension. So far, no problems.