Thing is, an average temperature of 100C isn’t enough, because that’s just an average. Even if the seas are boiling in parts of the planet, they’re still only temperate in other places.
So you have to get the temperature waaaaay over 100C, especially if you’re only using one rock. Any rock big enough to wipe out all life on the planet is going to be big enough to render the planet uninhabitable for a million years of so.
And after all life on the planet is extinct, after you’ve waited a million years…or 100,000 years…you still don’t have a habitable planet, because there’s no atmospheric oxygen left. You do know that oxygen comes from plants, right? Without plants making oxygen the atmosphere is going to be nitrogen, CO2, methane, ammonia, and other such things.
And you can’t just seed the place with plants, because plants need oxygen too. You’d have to dump anaerobic bacteria down there, wait for hundreds of thousands of years for them to colonize the planet, then try to establish cyanbacteria to start the photosynthetic cycle again. How many centuries do you want to wait?
There’s no such thing as a lifeless habitable planet. A lifeless planet requires that the humans there live in pressurized artificial environments. You might as well live on the Moon. Heck, the Moon would be easier, since you don’t have to worry about erosion and corrosion from the toxic atmosphere on your habitats.