A plug assembly for use in a key-operated lock, having a cylindrical key plug that can rotatable between a key insertion position and a control position, the key plug having a keyway and tumbler bores, an axial groove into the periphery displaced tangentially from the tumbler bores, a curved trough extending radially inwardly from the carriage groove, a control tooling slot formed radially inwardly from the curved trough. A carriage is moveable axially within the carriage groove, and has an outer surface proximate with the cylindrical periphery of the key plug. The carriage has radially-formed retainer bores that align tangentially with the tumbler bores when the carriage is in a position to accept lock configuration change balls. A separate change tooling blade can be inserted into the control tooling slot to raise any change balls within the retainer bores out through an outer opening the retainer bore.