Experimental measurements are performed to analyze the effects of passive control on a supersonic multi-stream rectangular nozzle. The configuration explored consists of a supersonic core stream (M = 1.6) and a sonic (M = 1) bypass stream which merge behind a splitter plate exiting into a Single Expansion Ramp Nozzle (SERN) and onto an aft-deck. Previous studies have deduced that the aft-deck geometry can alter the plume deflection and farfield acoustics, while the splitter plate has an influence on the shock train development and unsteady loading on the aft-deck due to the shedding instability behind the splitter plate. This campaign seeks to exploit the inherent receptivity of these regions by performing geometric modifications as a form of passive control. The study is broken down into two separate parts, the first being the aft-deck changes. Aft-decks explored vary parameters such as length, width, and chamfer from the nominal design to observe the influence of each on the flow. Comparison to the nominal, half nominal, and no deck cases are in agreement with previous studies and show the plume deflection being a result of the shock train development. All deck modifications showed a slight upward deflection of the jet plume. The second effort of this study is the exploration of a sinusoidal spanwise wavenumber to the splitter plate trailing edge. Experimental design of the splitter plate is guided by Large Eddy Simulations (LES) performed by The Ohio State University. Particle Image Velocimetry and farfield acoustics are recorded for a wavenumber of 0.8 to match that of the LES. Both simulations and experiments show a reduction in the dominating tone. Results from both forms of passive control are compared with and used for validation of simulations.