This investigation focused on the synthesis and characterization of a modified polyvinylsilazane (PVSZ) polymer. Previously, our group synthesized the PVSZ polymer through the ammonolysis of vinyltrichlorosilane (VTS) in tetrahydrofuran (THF). This material showed promise as a precursor for silicon nitride–silicon carbide-based ceramic materials. Due to the structure of the PVSZ polymer, the ability to stabilize (shelf-life) and dope with metals and metalloids has proven to be difficult. To overcome these problems, a second chlorosilane precursor, dichloromethylsilane, was introduced into the ammonolysis reaction. This polymer proved to be more stable (>3 months before cross-linking) and added a potential doping site on the backbone of the polymer while maintaining ceramic yields greater than 80%. The polymethylvinylsilazane (PMVSZ) polymer was characterized using attenuated total reflectance (ATR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and elemental analysis. The results indicated that the ratio of chlorosilane precursors used plays an important role in the composition of crystallized ceramic material.