It can be a big project when removing the old popcorn texture and applying new knockdown look, but the end results are well worth it. Knockdown is the modern look these days so it really adds a newer feeling to your home. It also makes the room seem a bit bigger because it has the effect of making the ceiling feel a bit higher. It reflects the natural light coming in through the windows much more effectively as well, showing off its details as the light shines across it. So, although popcorn texture can still look okay, knockdown tends to be more pleasing to the eye these days, and on top of all this, will boost the value of your home!
I've done a lot of repairs, and if there would be any issues with colour or texture matching afterwards I would let you know. If the texture is nice and white and away from the middle of the room where a lot of light shines in, then chances are it can be blended nicely if it's done right.
It is common in a lot of bathrooms with poor ventilation. In this case, the moisture accumulated in the skylight and caused the existing texture to easily fall off in flakes. What I did was scrape most of the skylight (left) where the texture was coming off easily, then sanded most of the surrounding area so that there would be no blending issues. Once it was all nice and smooth, I prepped the area for texture and applied knockdown. (right)
Very minimal to none. I cover everything with a layer of polyethylene plastic, sealing up any gaps and seams, using thorough techniques I've acquired over the years. When it's time to clean up, I do so in a manner that allows any falling mud or dust to be caught by the plastic on the floor, and roll everything up into a bundle once all is said and done. When all the garbage is out, I will go around with a damp cloth to get any minimal overspray. The idea is to always try to leave the job looking like I was never there, with the only difference being a new ceiling.