The conventional piano key weir (PKW), characterized by a rectangularly cranked planform, is an effective discharge structure. Its hydraulic performance is primarily influenced by several geometrical parameters, including crest length, key width, and weir height. To enhance its hydraulic efficiency, each key is modified with an isosceles triangle at both the crest and the vertical base surface. In this way, the weir crest is extended both up and downstream; the key floor is lowered accordingly, resulting in a triangular prism-shaped floor. Laboratory tests are conducted to compare the hydraulic performance of this modified weir with that of the standard design. The results demonstrate that the geometrical adjustments noticeably improve the overflow discharge. With an equilateral triangle extending the crest length by ~23%, the discharge capacity is enhanced by 16–20% within the examined flow conditions. The modified weir outperforms the conventional design in terms of hydraulic performance. The improvements can be attributed to several factors: elongated crest length enhancing the flow capacity; triangular upstream overhangs improving the inflow condition along the inlet key’s height; lowered inlet key floor increasing the flow volume, promoting better flow movement towards the crest; lowered outlet key floor reducing the submergence effect under high flow conditions; and the triangular crest of the inlet key facilitating jet spreading and promoting air entrainment. These modifications make the redesigned PKW a promising option for improved hydraulic performance in engineering applications.