It depends. The kinetic energy of the impact wouldn't be changed. The nature of the impact would be changed though. A pile of sand would probably transfer its kinetic energy into the atmosphere instead of impacting the ground. This could be good. But then, setting the atmosphere on fire might not be that great of an idea.

If the sand cloud has expanded enough before impact, then a large portion of it may miss earth entirely and therefore reduce the kinetic energy earth's atmosphere has to absorb.

As the post I was answering to just talked about converting the asterioid to sand, I assumed, that all of it would hit the atmosphere. But indeed, if in this way part of the asteroid misses the earth entirely, it would be a win. I was also a bit simplifiying/exaggerating. When talking about heating up the atmosphere, the consequences entirely depend on how high the thermal impact is going to be. If spread far enough, there could be a "global warming" which is below the limit for an instant disaster. (And when caused by a single event, would decay quickly)

Something else to potentially consider is the spread in the 'z axis', which would spread out the heating across time, not just space. Although I think that only helps if there is enough time for Earth to radiate a lot of that heat.

At large scales, asteroids beyond a few 100m, cohesion doesnt matter. It will travel through the atmosphere like a bullet through metal foil. It wont break up, instead punch a relatively clean hole.