n.

a component or accessory added to something after it has been manufactured

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

"the court ordered a retrofit on all automobiles"

RETROFITS
Carbon Capture Retrofits and the Cost of Regulatory Uncertainty
Existing building retrofits: Methodology and state-of-the-art
Evaluating sustainable retrofits in existing buildings under uncertainty
Optimum building energy retrofits under technical and economic;uncertainty
Design of FRPs in circular bridge column retrofits for ductility enhancement
Human-based energy retrofits in residential buildings: A cost-effective alternative to traditional physical strategies
Cost-benefit analysis and emission reduction of lighting retrofits in residential sector
Effects of Diesel Particle Filter Retrofits and Accelerated Fleet Turnover on Drayage Truck Emissions at the Port of Oakland
Process Plant Performance: measurement and data processing for optimization and retrofits