An enhanced process for shaping thermoset fiber-reinforced composites using Modified Double-Diaphragm Forming (mDDF) in Prepreg Compression Molding (PCM) is proposed to address limitations in conventional forming quality. To minimize surface defects, prepregs were pre-cut to reduce wrinkle formation and trimmed after preforming. Complex geometries were managed through draping analysis, which enabled identification and mitigation of wrinkle-prone regions. A challenging layup configuration (±45/0/90/0/90/0/±45) was selected, and temperature-dependent behavior of the prepreg—such as resin fluidity and wrinkle characteristics—was evaluated from room temperature to 80 °C. Material characterization included tensile, bias extension, bending, friction, and density tests. Forming simulations using AniForm Suite 3.0 incorporated fitted material parameters for predictive analysis. Experimental validation confirmed that the mDDF process significantly improved fiber alignment and eliminated wrinkle defects, especially in 16 previously identified critical zones. The final parts exhibited superior surface quality and dimensional accuracy compared to conventional PCM, highlighting the potential of mDDF for precision manufacturing of complex thermoset composite structures.