A rekeyable lock cylinder assembly includes at least one lock cylinder and a mortise lock adapter. Each lock cylinder includes a cylinder body with a longitudinal axis. A locking bar is disposed in the cylinder body for movement transverse to, and rotationally about, the longitudinal axis. A plug assembly having a tool receiving aperture is disposed in the cylinder body and is rotatable about the longitudinal axis. A plurality of pins and a corresponding plurality of racks are disposed in the plug assembly. A first member is moveable in response to application of a force by a tool received through the aperture to simultaneously disengage all of the plurality of racks from the plurality of pins. The mortise lock adapter includes a housing configured for receiving the cylinder body of the lock cylinder. A mortise lock actuator is coupled to the plug assembly of the lock cylinder.