Question regarding players switching on a free throw

[Jurassic Referee]

After a couple of times, I tell 'em "That's it. Pick a spot and don't move". If they want to ignore me and switch again, it's a "T" for delay under R10-3-6(a)- "delay the game by preventing the ball from being made live promptly...". That's good enough for me.

If a player goes across twice, that's when I'm putting a stop to it - at any level.