Text-changing effect

Text-changing effects change the text appearing in text box, type line, or name of a card. These effects are informally known as hacks or word-changers.

Description
Text-changing effects replace each instance of a characteristic, of a permanent or of a spell, with another of the same genus (e.g., color) or type (e.g., basic land subtype, creature subtype). Text-changing effects are considered exclusively within blue magic according to the historic and current understanding of the color pie, and all cards with a text-changing effect to date have been blue.

The term "hacks" has been recognized by at least Fifth Edition, by the Glossary of the Magic: The Gathering Official Strategy Guide.

Color word hacks
As of Theros Beyond Death, four (4) cards can change a color word to another:
 * (Alpha, Beta, Unlimited Edition, Revised Edition, Fourth Edition, Ice Age, Fifth Edition)
 * (Alpha, Beta, Unlimited Edition, Revised Edition, Fourth Edition, Ice Age, Fifth Edition)
 * (Alpha, Beta, Unlimited Edition, Revised Edition, Fourth Edition, Ice Age, Fifth Edition)
 * (Alpha, Beta, Unlimited Edition, Revised Edition, Fourth Edition, Ice Age, Fifth Edition)

Note that this ability is functionally different from those of color changers.

Basic land subtype hacks
As of Theros Beyond Death, one (1) card can change a basic land subtype to another:
 * (Alpha, Beta, Unlimited, Revised Edition, Fourth Edition, Fifth Edition)

Color word and/or basic land subtype hacks
As of Theros Beyond Death, five (5) cards can change a color word to another or a basic land subtype to another:
 * (Mirage, Eighth Edition, Ninth Edition, Tenth Edition)
 * (Mirage, Eighth Edition, Ninth Edition, Tenth Edition)

Creature subtype hacks
As of Theros Beyond Death, two cards can change a creature subtype with another:

Other hacks

 * Champions of Kamigawa featured Swirl the Mists, an enchantment that can replace all instance of color words in the text of spells and permanents with a chosen color word, chosen as it enters the battlefield.
 * Unhinged featured Magical Hacker, a creature that can replace plus ("+") signs in text boxes with minus ("−") signs and vice versa.