I have a map I'm working on where I run the "Switch Computer Player To Rescue Passive" AI script. Is there a way to turn it off with an other trigger later in game?

no

It would be fun if I could... Well, that's what I thought anyway.

Similar to the recent post about a map in which dead units are transferred to another player, if the rescued CPU was a difference race than the players normal race, you could give all units of that race to a different CPU player (with the same colour) to simulate this. This would also give units of that race that the player created to the CPU also, of course, which could be undesirable. But would make sense from a lore perspective with the Terrans enslaving the Zerg and then losing control (perhaps when an overmind/cerebrate killed as the trigger?).

Or, if the rescued base is separate from the player's main base, you could give all units/buildings at that area to a different CPU player. If you went this route you'd need to be careful that the player hadn't built up this new base as their main base, of course.

You can have a rescueable player as a reserve. Give units to the player when you need. Give them back to CPU when you don't.

Well, what I wanted was to be able to turn it on and off as much as I wanted. Since this is not possible, then I guess I can't do anything about it. (Unless I find out an other glitch and...)

What gigins meant was having 2 players with the same color. One active and one rescue passive. Whenever you want to activate the player give from rescue passive to active and vice versa.