There's no easy way to do it.

You need changetargets to change them one way, and more changetargets to change them back.

When you fire a changetarget it changes the target of the teleport from then on. You have to use another changetarget to change it back.

But that's not all.

You also need to trigger every other changetarget, every other round. You need changetargets for that too. You need something that gets triggered at the beginning of each round which fires off one of the sets of changetargets, and you need to use a changetarget on THAT to switch it each time.

It's almost impossible to explain but I hope I'm helping a little.

You can make your own entities all you want as long as you make your own MOD.

Changed targets stay changed at the new round.

You need to have two systems. One that runs on rounds 1, 3, 5, 7, ... and one that runs on rounds 2, 4, 6, 8, ...

There should be one "first cause" each round (I used a func_breakable under all the player starts) which triggers one of your systems.

You need to change the target of the first cause to the other system at the end of the logic in each system.