A method includes: mounting a rail on a wall; mounting a fixture on the rail by interlocking a channel of the fixture to the rail; removing the fixture from the rail; and mounting a replacement fixture on the rail by interlocking a channel of the replacement fixture to the rail. An apparatus has: a rail with a wall contacting base side, an exterior side, and a beam formed on the exterior side; a fixture with a base side, an exterior side, and a channel formed on the base side; and in which the channel forms a female profile that reversibly interlocks via a snap fit to a male profile formed by the beam to reversibly mount the fixture on the rail, with respective longitudinal axes of the beam and the channel extending in respective axial directions along the rail. The fixture and rail may retain a panel over the substrate.