From Longman Dictionary of Contemporary Englishretrofitret‧ro‧fit /ˈretrəʊfɪt $ -troʊ-/ verb (retrofitted, retrofitting) [transitive] to improve a machine, piece of equipment, building etc by putting new and better parts in it after it has been used for some time plans to retrofit oil boilers —retrofit noun [countable] —retrofitting noun [uncountable]→ See Verb table
Examples from the Corpus
retrofit• Some manufacturers are already offering to retrofit old models with catalytic converters.• The latest build is air-conditioned, and following the final deliveries Adtranz is to retrofit the earlier cars with full air-conditioning. 