Tailoring the surface properties of 2D materials, such as transition metal dichalcogenides (TMDCs), at the nanoscale is becoming essential in the fabrication of various 2D material-based nanoelectronic devices. Due to the chemical inertness of their basal plane, the surface modification of 2D TMDCs is limited to their defective sites, often requiring special treatments, such as the conversion of the TMDC from its semiconducting into its metallic phase. In this work, we show that the basal plane of a semiconducting 2D TMDC, molybdenum disulfide (MoS2) can be modified electrochemically by electrografting of aryl-diazonium salt. To demonstrate the advantages of this method at the nanoscale, we perform electrografting of 3,5-bis(trifluoromethyl)benzenediazonium tetrafluoroborate on predefined MoS2 nanoribbons by addressing them individually via a different electrode. The ability to selectively address individually contacted 2D layers opens the possibility for specific surface modification of neighboring 2D nanostructures by different functional groups. This method could be extended to other aryl-diazonium compounds, and other 2D semiconducting materials.