Stephenson:Neal:The System of the World:392:hot-swapped (JoelFinkle)

From the Quicksilver Metaweb.

"...almost the whole point of mistresses is that they may be hot-swapped."

Clearly an anachronism, as hot-swapped is commonly used to refer to replacement of parts, viz. hard disk drives in computers. It's possible it's been used for other items 'mechanikal' for a longer period, but still not within the 18th century, long before mass production enabled replaceable parts between similar engines.