If someone wants to be really sure, they could transfer the 800k thb in a calendar year when they are in Thailand 179 days or less.
I never planned to switch to 65k thb since I don't want to risk a monthly transfer not arriving on time etc. I keep a separate account for my daily spending and I don't bother with letting the balance drop below 800k. I try to keep my visa as simple as possible.
i am able to change the amount in my Bangkok Bank app. Hoping it stays that way. Luckily my landlord has (transfer)wise account, so I am able to pay him via that from my (transfer)wise account with funds from my USA bank or my singapore bank account. If your large payment is for rent, maybe this method will help you.