I tried it on a planet that I took BACK. But no one attacked the planet, so the trap never got tripped.

Should work. I would also put a Vortex Deflector on it.

The Abysmal trap triggers if someone attacks. The Deflector will prevent warping and bio-vaps. In theory, someone could bio-vaporize the population below 10, then invade and that wouldn't count as an "attack". I don't really know, but I also wouldn't risk it.

Bio vap cannot reduce pop below 10.

OK. should work then. I've never used the bio-vaps below a few hundred pop. At what point do they not cut the population in half?

it will work.
youre safe.

I've done it and seen it done a few times.

Bio vaporizers used to drop it below 10 so we could bypass rift traps but Dan fixed that. Now you have to attack the planet for it to go under 10 to invade. Blame wolfy for that suggestion.

No, you can't invade a planet with an active rift trap even if the shot that sets it off puts you under 10.

However it is entirely possible that this could be bypassed if he planet was under a lot of actions at once like when you steal a planet and the opposing legion is guarding the planet still.
If that did happen I'm sure Dan would just return the planet.