RockShox Monarch rear shocks are not convertible to remote lockout or vice versa. Remote adjust shocks versus manual adjust are internally different. A remote adjust shock relies on the remote lever itself to hold the shock in the open or locked position. The shock damper is spring-loaded to adjust back after the remote is actuated.
A manual shock uses detents in the actuator and has no spring to pull through the settings. Because of the differences in how lockout is achieved, it is not possible to change from remote to manual.