1: to furnish (something, such as a computer, airplane, or building) with new or modified parts or equipment not available or considered necessary at the time of manufacture
2: to install (new or modified parts or equipment) in something previously manufactured or constructed
https://www.merriam-webster.com/dictionary/retrofit
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verb (used with object), ret·ro·fit·ted or ret·ro·fit, ret·ro·fit·ting.
to modify equipment (in airplanes, automobiles, a factory, etc.) that is already in service using parts developed or made available after the time of original manufacture.
to install, fit, or adapt (a device or system) for use with something older:
to retrofit solar heating to a poorly insulated house.
verb (used without object), ret·ro·fit·ted or ret·ro·fit, ret·ro·fit·ting.
(of new or modified parts, equipment, etc.) to fit into or onto existing equipment.
to replace existing parts, equipment, etc., with updated parts or systems.
https://www.dictionary.com/browse/retrofit



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Naval vessels often undergo retrofitting in dry dock to incorporate new technologies, change their operational designation, or compensate for perceived weaknesses in their design or gun plan.
https://en.wikipedia.org/wiki/Retrofitting
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