Something that has been retrofitted
The act of retrofitting
To add or substitute new parts or components to some device, structure etc., that were not previously available; to modernize
To fix an older version (or older versions) as part of the same process of fixing the newest version; to backport
The bug was so bad that we had to retrofit our patch to the last three releases, as well as the newest release.
Of, relating to, or being a retrofit