Metal/semiconductor Au/Ag2S core/shell hetero-nanorods with controlled morphology are synthesized and their tunable plasmon enhancements (involving linear and nonlinear optical processes) are demonstrated. The synthesis involves site-selective deposition of Ag layer onto Au nanorod seeds, followed by site-selective sulfuration of the Ag layer, resulting in three types of Au/Ag2S core/shell nanorods with complete, corner-opened, or end-opened shells. The plasmon resonance and local field confinements varing with shell morphology are analyzed using FDTD calculations. Nonlinear measurements reveal that the Ag2S shell with appropriate morphology leads to the nonlinear refraction and saturable intensity of the Au nanorods increasing 7.6 and 4.1 times, respectively, which indicates strong plasmon enhancements and energy relaxation in the Au/Ag2S core/shell nanorods. This site-selective shell growth strategy offers a constructive bottom-up approach to maneuver the optical properties of plasmonic nanocrystals for various applications.