The correct answer is C) replacing the propellant cartridge and refilling with powder. To recharge a previously used cartridge-operated dry-chemical extinguisher, the propellant cartridge must be replaced, and the extinguisher must be refilled with the appropriate dry-chemical powder. This is a required procedure outlined in the regulations governing the servicing and maintenance of portable fire extinguishers. The other options are incorrect because: A) simply recharging the cartridge is not sufficient, the powder must also be refilled; B) puncturing the cartridge seal is not a proper recharging procedure; and D) while authorized fire equipment servicing personnel must perform the recharging, this does not directly address the specific steps required.