You really should reapply thermal paste/grease every time you remove the heatsink from the cpu. it guarentees there are no air bubbles so you get good contact.
i used an air compressor, it is fine aslong as you intend to remove the fan from the heatsink and the heatsink from the cpu ( which would require regreasing)
i did this and no word of a lie, i cannot see a spec of dust on my heatsink.... good as new
so in conclusion to the thread title, this method is arguably the best (leaves no dust behind whatsoever) and the safest ( no risk of damage to components or fans)
just make sure you have a tube of thermal grease before you do this