Reaction-bonded silicon carbide (RB-SiC) ceramics are critically important for applications in space optics and precision manufacturing due to their excellent thermophysical properties and near-net-shape capability. However, their high hardness, brittleness, and multi-phase composite structure (consisting of multi-sized SiC grains and free silicon) classify them as typical difficult-to-machine materials. To address the specific structure of RB-SiC, this study proposes a femtosecond laser selective processing strategy. By switching between a galvanometer-objective lens system (with a spot diameter of 4 μm) and a galvanometer-field lens system (with a spot diameter of 28 μm), selective microtexturing and high-efficiency planarization of RB-SiC are achieved, respectively. Experimental results indicate that under low energy density, the objective lens system enables the selective removal of free Si and submicron SiC particles while preserving the large SiC skeleton structure on the scale of tens of micrometers. Conversely, under high energy density, the field lens system produces smooth microgrooves with a surface roughness Ra < 1.5 μm and a removal depth >270 μm. The combination of these two processing methods facilitates the creation of functional micro-structured surfaces. By integrating dual-temperature model simulations with multiple characterization techniques, the interaction mechanism between laser parameters and the material's multi-phase structure was systematically elucidated, clarifying the physical principles underlying selective material removal. This work provides new insights and key technical support for the laser-based precision machining of multi-phase composite materials.