The swap, which will be in effect for one week in February, is part of a push to promote the release of Game of Thrones season three on DVD.
An HBO producer reportedly got the idea while waiting for a train in London's Euston station and heard the town listed as a stop.
Kings Langley is about 25 miles northwest of London. Kings Landing, which lies on the western coast of Westeros and will go back to being strictly fictional by March, is the seat of power in the fantasy show and the series of novels by George R.R. Martin.