Definitions of retrofit:

• noun:   the act of adding a component or accessory to something that did not have it when it was manufactured

  Example: "The court ordered a retrofit on all automobiles"

• noun:   a component or accessory added to something after it has been manufactured
• verb:   provide with parts, devices, or equipment not available or in use at the time of the original manufacture

  Example: "They car companies retrofitted all the old models with new carburetors"

• verb:   substitute new or modernized parts or equipment for older ones

  Example: "The laboratory retrofitted to meet the safety codes"

• verb:   fit in or on an existing structure, such as an older house

  Example: "The mansion was retrofitted with modern plumbing"