This is another one of those old baseball/softball rule myths rearing its ugly head again...
There's no limit to how many times a batter can switch from one box to the other during an at-bat, and no special ball/strike count that prevents them from switching.
What you can't do is step directly from one box to the other once the pitcher has the ball and is on the pitcher's plate in position to pitch. You will be called out. So, if you want to switch either ask for time first and wait until it's granted, or do it before the pitcher is ready to pitch.