A key-removable lock core that is retained in a core receptacle by a retaining lug, and which can operated by an operating key to align the pins of the pin chambers for shear at the operating shear line, and to allow the key plug to be rotated, and which employs a control tool with the operating key for manipulating the pins into alignment for shear at the control shear line, to allow the sleeve and the key plug together to be rotated, to move the retaining lug on the sleeve between a projected position in which the lug is engaged behind a rearward-facing shoulder in the core receptacle to retain the core in the receptacle, and a retracted position within the profile of the core.