Embodiments disclosed in the detailed description include supporting an add-on remote unit(s) (RU) in an optical fiber-based distributed antenna system (DAS) over existing optical fiber communications medium using radio frequency (RF) multiplexing. An existing DAS comprises at least one existing head end equipment (HEE) communicatively coupled to a plurality of existing RUs through an existing optical fiber communications medium. In aspects disclosed herein, an add-on RU is added to the existing DAS to support additional wireless communications. No new optical fibers are required to be deployed to support communications to the add-on RU in the existing DAS. Instead, the existing DAS is configured to support the add-on RU through the existing optical fiber communications medium using RF multiplexing. As a result, the add-on RU can be added to the existing optical fiber-based DAS without adding new optical fibers, thus leading to reduced service disruptions and deployment costs.