If the old paint isn’t peeling, new paint on top won’t damage it. HOWEVER, the new paint might not adhere well to the old stuff, and peel off in a year or two. In my opinion, best practice is to scrape any loose paint off, and sand the edges of the painted areas smooth. Prime the areas to be painted (it will help new paint adhere to old), then finally paint the areas with new paint.
If the old paint isn’t peeling, new paint on top won’t damage it. HOWEVER, the new paint might not adhere well to the old stuff, and peel off in a year or two. In my opinion, best practice is to scrape any loose paint off, and sand the edges of the painted areas smooth. Prime the areas to be painted (it will help new paint adhere to old), then finally paint the areas with new paint.