You don't need to inform the bank. Just carry on and you will be fine. If you use an atm you will likely be charged an out of province fee. But QR etc will all work the same with no extra charge.
never heard of that and believe it's an urban myth. It's not as if they do that with retirement or marriage. Just never encountered it or know anyone that has
I arrived from Cambodia to BKK early this morning. No issues at all, quick stamp and out of there. I go to Cambodia every couple of months. Never had an issue