What conditions do you need for runaway greenhouse effect at 1 AU. earth has had over 20% CO2 in the past, but the sun was cooler then.

Moving the planet and pulverising with an impact large enough to kill everything are firmly in the bounds of not currently feasible.

I really doubt humans could do it, it would have to be done in one fell swoop, because any attempt to push the earth beyond a tipping point for bacteria to be killed would require pushing for longer than we, the pushers, could survive.

We would have to be better at designing than evolution to make Grey Goo, otherwise evolution would probably have already done it, and it has, to date, designed some pretty out there things.