Will this molding fit over my existing bumper, or do I need to remove the bumper first?

Mounting method isn't confirmed in the product specs — test-fit the trim against your bumper and existing attachment points before final installation. You may be able to secure it without bumper removal, but have a helper on hand to check alignment.

Does satin chrome scratch easily?

ABS with a satin chrome finish is durable for normal use, but like any trim, it can scuff if contacted hard. The satin texture hides minor marks better than polished chrome would.

Can I paint this, or does it need to stay chrome?

Satin chrome is designed as a finished product. If you want to change the color, test adhesion on a hidden area first — ABS can be prepped and painted, but primer choice and surface prep aren't specified here, so confirm compatibility with your paint system before committing.