The story
17th century; origin uncertain, but possibly from transmigure, transmigrate. It is also possible that this word is a formation derived from maugre, hence it originally signified the "evil eye", but under the influence of the former etymologies shifted its meaning to its sense of "transformation". Another possibility is a humorous blending of transfigure and modify.
Etymology from Wiktionary, CC BY-SA 4.0.