Painting - Can I paint over Riveted Wood Shakes without scraping off old paint?

I'm not trying to be lazy but I'm being told by Paint Contractors that they are impossible to scrape. They aren't just normal cedar shakes, they have raised peaks and valleys on them so you would have to scrape in between every little crack on every shake.

If the paint isn't peeling on the shakes, couldn't I just wash them really well, let them dry for a few days, prime them, and paint over them with a new color??

I was also told not to pressure wash shakes because it will loosen them. Any painting pros out there that have advice??

Due to the heavy texture, shakes present various problems. There are several blasting techniques if they are peeling badly, walnut shells, baking soda, Etc. I think if you vertically scrape and wirebrush them to remove the loose and scaling paint, you can do a fair job. Generally though, when shingles or shakes are peeling so bad, they are cracking horizontally against the grain, it is time to replace them. If you try to pressure wash them and they become loose, but the desired amount of paint comes off, just re-nail them back. If they fly off, again, likely time to replace the siding. You sometimes have to balance the cost of stripping and replacing them, with the coat of preparing them to be saved in order to make a good decision. I have an old 1895 house with the original clapboards with paint on them 1/4" thick, and at times peeling badly. Little by little over the years, one side at a time, I've replaced them. The house looks brand new now.

Bill