According to Dmitri Borgmann's "Language on Vacation," metallege is a psychological term which has been adapted by logology to describe word pairs such as SALVE and SLAVE, or SKATE and STAKE. Perhaps a more descriptive term would be letter-swap transposals.
"A Classificiation of Metalleges,"
Word Ways: Vol. 24
, Article 12.
Available at: http://digitalcommons.butler.edu/wordways/vol24/iss1/12