to use scripting to create the effect below:

1.when you reach a corner you can shrink into the shadows, and become invisible, but not move.
2.when you reach any kind of barrier you can crouch behind it.
3.when you come to a metal beam crossing a gap, you can grip the beam and swing across

I realize that it would involve a lot of vehicles. Suggestions?

1) Enter a trigger volume
Spawn an active camouflage, that has no pickup sound, no pickup effect.
player_enable_input false

at the press of the action button, though?

Then that would be a vehicle or something. Set it to not show the driver.