The factory trim strip, for the most part, is applied with strong adhesive tape. The only exception is the rear bed corner, if I remember correctly, the bed corner trim piece has studs on the backside that go through the bedside.
Changing mirror is fairly easy. If you have the larger stainless mirrors, you'll likely be filling holes.
How fresh is the black paint? With a new coat of paint next to an old coat it might look good or you may get it out of the paint shop and see all the flaws in the current black paint.