In a turbine rotor blade having a platform at an interface between an airfoil and a root, wherein the airfoil and the root include an interior cooling passage formed therein, wherein, in operation, the interior cooling passage comprises at least a high-pressure coolant region and a low-pressure coolant region, platform cooling arrangement that includes: a platform slot extending circumferentially from a mouth formed through the pressure side slashface; a high-pressure connector that connects the platform slot to the high-pressure coolant region of the interior cooling passage; a low-pressure connector that connects the platform slot to the low-pressure coolant region of the interior cooling passage; and a platform cooling cartridge removably engaged within the platform slot, the platform cooling cartridge comprising one or more cartridge cooling channels.