Try playing with /set update_k. In addition to making the bots invisible, it also messes up sound. Does it have an actual purpose?

k stands for "Kapwing!" I think, considering what it did when you and FiReMaGe were messing with it earlier this week. :P

Weird that it messes up the sound.
It's used for the dead-reckoning of other ships on your client.

Set it to positive 1000 and sound has a nice 5 second lag. And turbo sound doesn't come on at all. My question is, am I invincible with it?

it's purely a client-side passive option that doesn't affect the server at all.

It only affects how you perceive other moving objects in the game. It's the smoothing constant, and it follows an exponential curve. It's been in there for years and years. So yeah, you can set it to... anything above 1 and then get killed by bots that you don't see. The default value is -3.5. I suggest you leave it there.