Trying to install a tap on an active fiber cable sounds like a very much impossible feat for any kind of modern technology. If I was the poor EE they laid this

Trying to install a tap on an active fiber cable sounds like a very much impossible feat for any kind of modern technology. If I was the poor EE they laid this problem on, I would have the submarine install the tap while the cable is still being laid, before it's connected to any data streams. Without knowing how long it takes to install the tap, it would also be possible to sabotage cables, install the tap while the cable is down, and make the sabotage out to be the doings of any number of semi-rogue countries in your targeted part of the world.