Retconjuration is a theoretical branch of magic. No ordinary caster can practice it; there are no Retconjurers in Erfworld. It is reserved for the Titans. They don't like it much and use it as seldom as possible.
Retconjuration is a theoretical school of magic and one of the three disciplines of the Magic class Naughtymancy; it is aligned with the axis of Numbers and composed of the two elements of Motion and Matter. Erf-b1-p038a
This school of magic allows past events to be changed to mesh with current needs. It is theorized that only the Titans have access to the powers of Retconjuration as it is too powerful for a mere mortal to comprehend even its smallest of ramifications. Being a very volatile subject, it is usually avoided in most public forums and viewpoints on the subject differ greatly.
Mortal users of Retconjuration would be in position to engage each other in a war of existential reconstruction, up to the point that only a timeline where they were all erased would be stable. Of course, as there have been no mortal Retconjurers, then either this is impossible or it has already happened.
(Alternatively, it may be possible that there is one Retconjurer far in the future, who managed to remove all the others except him or herself.)
Things that have been Retconned
The school of Retconjuration is notable for being an example of itself; the Numbers axis of Naughtymancy was an entirely different school called "Deletionism" the-ultimate-naughtymancy until the Titans realized that Retconjuration would be necessary for them to properly maintain Erfworld. As a removed school of magic, this also kind of makes Deletionism an example of itself.
One line of fan speculation postulates that there could be a Retconjuration war going on between the Titans, with one faction backing Stanley the Tool's bid to overthrow royalty and unite the Arkentools, and the other opposing it. So far, the side opposing Stanley has left an extra gem in a Marbit mine, leading to Stanley's defeat at the Battle of Warchalking, and the other has caused Lookamancers and Findamancers to research the "Summon Perfect Warlord" spell, or possibly provided Parson's glasses, bracer and sword, leading to the defeat of the Royal Crown Coalition.
Real World References
The name refers to "retcon", short for "retroactive continuity", in which the history of a fictional setting is changed after publishing to mesh better with the current desires of the author. Ironically, Retconjuration is itself the product of a retcon; the Naughtymancy class previously aligned with Numbers was known as "Deletionism" before it was replaced with Retconjuration.