A wall panel arrangement is adapted to be used in a wall panel system provided with at least one pair of spaced apart vertical frame members having inwardly facing sidewalls for retaining at least one existing panel therebetween. The wall panel arrangement includes an add-on wall panel assembly constructed with opposed face structure connected to opposed side structure, and adapted to cover at least a portion of the existing panel. Mounting structure is provided on the wall panel assembly, and is configured with flexible resilient retainers extending outwardly relative to the side structure, and adapted to frictionally engage the inwardly facing flat walls of the vertical frame members, and hold the wall panel assembly over the existing panel and between the vertical frame members.