Can I paint over a topcoat?

Yes, you can paint over a topcoat, and it is common to do so when repainting walls, changing color, or refreshing finish, but you need proper preparation for good adhesion. If existing topcoat is in good condition, clean, matte, and well adhered, you can paint over it after cleaning surface with soap and water to remove grease and dust, lightly sanding with fine 220 grit sandpaper to degloss and create key for new paint to grip, wiping dust, then applying new primer if needed for drastic color change or stains, then new topcoat. If existing topcoat is glossy, oil based, or you are switching from oil to latex, you must sand to dull gloss and apply bonding primer, otherwise new paint may peel. If existing topcoat is peeling, cracking, or chalky, you must scrape loose paint, sand edges, fill holes, and prime bare spots before painting over. For wood, lightly sand topcoat before new topcoat. For cars, you can paint over existing clear topcoat after sanding and priming. So yes, you can paint over a topcoat, but clean, sand lightly, and prime if needed for glossy, stained, or drastic color change to ensure adhesion and durable finish.