Powder coating is for metal. The metal gets hooked up to a power source that makes it electrically charged. Then when the plastic powder is sprayed on, it gets attracted to the charge. Then the part gets baked in an oven to melt the plastic particles together. I'd think that last part could be difficult without warping the plastic part to begin with.

When sanding, the method for getting a perfect result is to use progressively finer sandpaper, with a cleaning in-between each. Each successive step should be with less than twice the grit than the step before.

An auto repair shop could use paints that are a bit more durable and stand up to prolonged use more than what is easy to buy and use as a hobbyist.

I think I would have just spray it with black spray paint, if I did it. The first thing to think about to get a good result is to spray even thin layers and let each one dry before the next.
My long-term daily driver is spray-painted, and the paint on it is very worn by now. I was going to repaint it years ago but couldn't find a new can of the same type ... I'm on the lookout for a "vintage beige computer" spray paint.

Following this thread to see how it worked out.  I have 2 of these tops that have gone all sticky and are deteriorating.  I usually just swap out to a new top    But now I'm on my last one!  I did sand down and paint a CM board but I don't think it was the rubberized version.  I will say... if you plan to hand sand and paint it, you really need to be meticulous about sanding.  You will probably see any swirl marks left from the sanding when you paint.

I would prefer powder coating but that is not so popular done on plastic. So would need to take it to car repair and get them to paint it, like few layers.

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